Google 2026 LeetCode Interview Preparation Guide

Arrays & Strings
Two Pointers & Sliding Window
Hash Maps & Sets
Stack & Queue
Linked Lists
Trees & Binary Search Trees
Trie (Prefix Tree)
Graphs & BFS/DFS
Dynamic Programming
Backtracking
Heap & Priority Queue
Binary Search
Intervals
Greedy Algorithms
Bit Manipulation
Design Problems
Recursion
Sorting & Searching
Math & Geometry
Advanced Topics

Arrays & Strings

Easy

1. Two Sum - Classic hash map problem, foundation for many others
26. Remove Duplicates from Sorted Array - Two pointer in-place modification
27. Remove Element - In-place array manipulation
53. Maximum Subarray - Kadane's algorithm
66. Plus One - Array carry propagation
88. Merge Sorted Array - Two pointer merge from end
118. Pascal's Triangle - 2D array generation
121. Best Time to Buy and Sell Stock - Single pass tracking minimum
169. Majority Element - Boyer-Moore voting algorithm
217. Contains Duplicate - Hash set usage
242. Valid Anagram - Frequency counting
268. Missing Number - Multiple approaches (XOR, math, sorting)
448. Find All Numbers Disappeared in Array - In-place marking technique
605. Can Place Flowers - Greedy placement checking

Medium

3. Longest Substring Without Repeating Characters - Classic sliding window
5. Longest Palindromic Substring - Expand around center
11. Container With Most Water - Two pointers greedy
15. 3Sum - Two pointers with sorting, duplicate handling
16. 3Sum Closest - Two pointers variant
18. 4Sum - Extension of 3Sum pattern
31. Next Permutation - Array rearrangement in-place
33. Search in Rotated Sorted Array - Modified binary search
36. Valid Sudoku - Hash set validation
48. Rotate Image - Matrix manipulation in-place
49. Group Anagrams - Hash map with sorted key
54. Spiral Matrix - Boundary tracking pattern
55. Jump Game - Greedy reachability
56. Merge Intervals - Interval merging
75. Sort Colors - Dutch national flag (3-way partition)
128. Longest Consecutive Sequence - Hash set O(n) solution
152. Maximum Product Subarray - DP tracking min and max
167. Two Sum II - Two pointers on sorted array
189. Rotate Array - Reversal algorithm
238. Product of Array Except Self - Prefix/suffix product technique
287. Find the Duplicate Number - Floyd's cycle detection
289. Game of Life - In-place state encoding
334. Increasing Triplet Subsequence - Greedy two variable tracking
347. Top K Frequent Elements - Bucket sort or heap
560. Subarray Sum Equals K - Prefix sum with hash map
739. Daily Temperatures - Monotonic stack pattern

Hard

4. Median of Two Sorted Arrays - Binary search partition
41. First Missing Positive - In-place hashing
42. Trapping Rain Water - Two pointers or stack approach
76. Minimum Window Substring - Sliding window with frequency map
84. Largest Rectangle in Histogram - Monotonic stack
85. Maximal Rectangle - Extension of histogram
239. Sliding Window Maximum - Deque for maintaining window maximum

Two Pointers & Sliding Window

Easy

125. Valid Palindrome - Basic two pointer technique
283. Move Zeroes - In-place array manipulation
344. Reverse String - Foundation for string manipulation
392. Is Subsequence - Two pointer matching

Medium

3. Longest Substring Without Repeating Characters - Classic sliding window
11. Container With Most Water - Two pointers with greedy choice
15. 3Sum - Two pointers after sorting
424. Longest Repeating Character Replacement - Sliding window with character count
438. Find All Anagrams in String - Fixed window sliding
567. Permutation in String - Fixed-size sliding window with frequency matching
713. Subarray Product Less Than K - Sliding window with product

Hard

30. Substring with Concatenation of All Words - Complex sliding window
76. Minimum Window Substring - Variable-size window optimization
239. Sliding Window Maximum - Deque technique

Hash Maps & Sets

Easy

1. Two Sum - Hash map for O(n) lookup
13. Roman to Integer - Hash map lookup
217. Contains Duplicate - Basic set usage
242. Valid Anagram - Frequency map
383. Ransom Note - Frequency counting
387. First Unique Character in String - Frequency counting

Medium

49. Group Anagrams - Hash map with sorted key or frequency tuple
128. Longest Consecutive Sequence - Set for O(1) lookups
146. LRU Cache - Hash map + doubly linked list
380. Insert Delete GetRandom O(1) - Array + hash map combination
454. 4Sum II - Hash map to split problem
560. Subarray Sum Equals K - Prefix sum hash map

Hard

895. Maximum Frequency Stack - Nested hash maps with frequency tracking

Stack & Queue

Easy

20. Valid Parentheses - Classic stack problem
225. Implement Stack using Queues - Queue simulation
232. Implement Queue using Stacks - Stack simulation
496. Next Greater Element I - Monotonic stack intro

Medium

150. Evaluate Reverse Polish Notation - Stack for expression evaluation
155. Min Stack - Stack with auxiliary structure
227. Basic Calculator II - Stack for operators
394. Decode String - Nested bracket handling with stack
503. Next Greater Element II - Circular array with stack
739. Daily Temperatures - Monotonic stack for next greater element
853. Car Fleet - Stack with sorting
901. Online Stock Span - Monotonic stack

Hard

84. Largest Rectangle in Histogram - Monotonic stack pattern
85. Maximal Rectangle - Extension of histogram problem
224. Basic Calculator - Stack with parentheses

Linked Lists

Easy

21. Merge Two Sorted Lists - Basic linked list manipulation
83. Remove Duplicates from Sorted List - Single pass removal
141. Linked List Cycle - Floyd's cycle detection
160. Intersection of Two Linked Lists - Two pointer alignment
203. Remove Linked List Elements - Node removal
206. Reverse Linked List - Iterative and recursive approaches
234. Palindrome Linked List - Find middle and reverse
876. Middle of the Linked List - Fast/slow pointers

Medium

2. Add Two Numbers - Carry handling in linked lists
19. Remove Nth Node From End - Two pointer technique
24. Swap Nodes in Pairs - Pointer manipulation
61. Rotate List - Find length and reconnect
86. Partition List - Two list splitting
92. Reverse Linked List II - Partial reversal
138. Copy List with Random Pointer - Hash map for node cloning
142. Linked List Cycle II - Floyd's cycle detection with start
143. Reorder List - Find middle, reverse, merge
146. LRU Cache - Doubly linked list implementation
148. Sort List - Merge sort on linked list

Hard

23. Merge k Sorted Lists - Heap or divide-and-conquer
25. Reverse Nodes in k-Group - Complex pointer manipulation

Trees & Binary Search Trees

Easy

94. Binary Tree Inorder Traversal - Recursive and iterative
100. Same Tree - Tree comparison recursion
101. Symmetric Tree - Mirror checking
104. Maximum Depth of Binary Tree - Simple DFS/BFS
108. Convert Sorted Array to BST - Balanced BST construction
110. Balanced Binary Tree - Height checking
111. Minimum Depth of Binary Tree - BFS or DFS
112. Path Sum - Root to leaf path
226. Invert Binary Tree - Classic tree recursion
235. Lowest Common Ancestor of BST - BST property usage
257. Binary Tree Paths - Path collection
543. Diameter of Binary Tree - Path through nodes
572. Subtree of Another Tree - Tree matching
617. Merge Two Binary Trees - Tree merging

Medium

95. Unique Binary Search Trees II - Generate all BSTs
96. Unique Binary Search Trees - Catalan number DP
98. Validate Binary Search Tree - BST property checking
102. Binary Tree Level Order Traversal - BFS with queue
103. Binary Tree Zigzag Level Order - BFS with alternating direction
105. Construct Binary Tree from Preorder and Inorder - Tree reconstruction
106. Construct from Inorder and Postorder - Tree reconstruction variant
113. Path Sum II - All root-to-leaf paths
114. Flatten Binary Tree to Linked List - In-place flattening
116. Populating Next Right Pointers - Level linking
117. Populating Next Right Pointers II - General tree variant
124. Binary Tree Maximum Path Sum - Post-order with global maximum
129. Sum Root to Leaf Numbers - Path sum calculation
144. Binary Tree Preorder Traversal - Iterative preorder
173. BST Iterator - Controlled inorder traversal
199. Binary Tree Right Side View - Level order last element
222. Count Complete Tree Nodes - Binary search on tree
230. Kth Smallest Element in BST - Inorder traversal
236. Lowest Common Ancestor - Classic tree recursion
297. Serialize and Deserialize Binary Tree - Tree encoding/decoding
337. House Robber III - Tree DP
450. Delete Node in BST - BST deletion
508. Most Frequent Subtree Sum - Hash map with DFS
513. Find Bottom Left Tree Value - Level order traversal
515. Find Largest Value in Each Row - Level order max tracking
662. Maximum Width of Binary Tree - BFS with indexing
1448. Count Good Nodes - DFS with max tracking

Hard

124. Binary Tree Maximum Path Sum - Path through node consideration
145. Binary Tree Postorder Traversal - Iterative postorder
297. Serialize and Deserialize Binary Tree - Complete tree serialization
987. Vertical Order Traversal - Complex sorting with coordinates

Trie (Prefix Tree)

Easy

14. Longest Common Prefix - String prefix comparison (can use Trie)

Medium

208. Implement Trie - Basic Trie implementation
211. Design Add and Search Words - Trie with wildcard search
648. Replace Words - Trie for finding shortest prefix
677. Map Sum Pairs - Trie with value aggregation
720. Longest Word in Dictionary - Trie building with validation
1268. Search Suggestions System - Trie for autocomplete

Hard

212. Word Search II - Trie + backtracking on 2D board
421. Maximum XOR of Two Numbers - Binary Trie for XOR
472. Concatenated Words - Trie with word break
1233. Remove Sub-Folders - Trie for folder paths

Graphs & BFS/DFS

Easy

463. Island Perimeter - Grid traversal counting
733. Flood Fill - Basic DFS/BFS
997. Find the Town Judge - In-degree/out-degree

Medium

130. Surrounded Regions - DFS from boundary
133. Clone Graph - Graph cloning with hash map
200. Number of Islands - Connected components
207. Course Schedule - Cycle detection (topological sort)
210. Course Schedule II - Topological ordering
261. Graph Valid Tree - Union-find or DFS
286. Walls and Gates - Multi-source BFS
310. Minimum Height Trees - Tree center finding
323. Number of Connected Components - Union-find
417. Pacific Atlantic Water Flow - DFS from boundaries
433. Minimum Genetic Mutation - BFS shortest path
684. Redundant Connection - Union-find cycle detection
695. Max Area of Island - DFS with size tracking
721. Accounts Merge - Union-find with strings
743. Network Delay Time - Dijkstra's algorithm
785. Is Graph Bipartite - BFS/DFS coloring
797. All Paths From Source to Target - Backtracking in DAG
841. Keys and Rooms - DFS reachability
994. Rotting Oranges - Multi-source BFS with time
1020. Number of Enclaves - DFS from boundary
1091. Shortest Path in Binary Matrix - BFS 8-directional
1306. Jump Game III - BFS/DFS reachability

Hard

127. Word Ladder - BFS shortest path
126. Word Ladder II - BFS + backtracking
269. Alien Dictionary - Topological sort
329. Longest Increasing Path in Matrix - DFS with memoization
787. Cheapest Flights Within K Stops - Modified Dijkstra/Bellman-Ford
778. Swim in Rising Water - Binary search + BFS or Dijkstra

Dynamic Programming

Easy

70. Climbing Stairs - Basic 1D DP
118. Pascal's Triangle - 2D DP pattern
119. Pascal's Triangle II - Space optimized
121. Best Time to Buy and Sell Stock - State machine DP
338. Counting Bits - DP with bit manipulation
509. Fibonacci Number - Classic DP intro
746. Min Cost Climbing Stairs - 1D DP variant

Medium

5. Longest Palindromic Substring - 2D DP or expand around center
22. Generate Parentheses - DP or backtracking
45. Jump Game II - Greedy or DP
55. Jump Game - Greedy reachability
62. Unique Paths - 2D grid DP
63. Unique Paths II - Grid DP with obstacles
64. Minimum Path Sum - Grid path DP
91. Decode Ways - 1D DP with transitions
120. Triangle - Bottom-up DP
139. Word Break - 1D DP with substring checking
152. Maximum Product Subarray - Track min and max products
198. House Robber - Classic DP pattern
213. House Robber II - Circular array variant
221. Maximal Square - 2D DP for max square in matrix
279. Perfect Squares - Complete knapsack variant
300. Longest Increasing Subsequence - O(n log n) with binary search
309. Best Time to Buy and Sell Stock with Cooldown - State machine DP
322. Coin Change - Classic unbounded knapsack
337. House Robber III - Tree DP
377. Combination Sum IV - Permutation DP
416. Partition Equal Subset Sum - 0/1 knapsack
435. Non-overlapping Intervals - Interval scheduling (greedy/DP)
494. Target Sum - Subset sum DP
516. Longest Palindromic Subsequence - 2D DP
518. Coin Change II - Combination DP
647. Palindromic Substrings - Expand around center or DP
673. Number of Longest Increasing Subsequence - LIS variant with count
714. Best Time to Buy and Sell Stock with Fee - State machine DP
718. Maximum Length of Repeated Subarray - 2D DP for subarray
746. Min Cost Climbing Stairs - Basic DP with cost
931. Minimum Falling Path Sum - Grid path DP
1035. Uncrossed Lines - LCS variant
1143. Longest Common Subsequence - Classic 2D DP

Hard

10. Regular Expression Matching - 2D DP with wildcards
32. Longest Valid Parentheses - Stack or DP approach
44. Wildcard Matching - 2D DP pattern matching
72. Edit Distance - Classic string DP
97. Interleaving String - 2D DP with two pointers
115. Distinct Subsequences - Count subsequences DP
123. Best Time to Buy and Sell Stock III - Multiple transactions DP
132. Palindrome Partitioning II - 2D DP minimum cuts
140. Word Break II - DP with backtracking
188. Best Time to Buy and Sell Stock IV - K transactions DP
300. Longest Increasing Subsequence - Binary search optimization
312. Burst Balloons - Interval DP
329. Longest Increasing Path in Matrix - DFS with memoization
410. Split Array Largest Sum - Binary search + DP
446. Arithmetic Slices II - Hash map DP
472. Concatenated Words - Word break with Trie
514. Freedom Trail - 2D DP with rotation
517. Super Washing Machines - Greedy/DP flow
639. Decode Ways II - DP with wildcards
664. Strange Printer - Interval DP
801. Minimum Swaps To Make Sequences Increasing - State DP
1000. Minimum Cost to Merge Stones - Interval DP
1388. Pizza With 3n Slices - Circular array DP

Backtracking

Easy

17. Letter Combinations of Phone Number - Basic backtracking template
401. Binary Watch - Generate combinations

Medium

17. Letter Combinations of Phone Number - Phone keypad combinations
22. Generate Parentheses - Valid combinations generation
39. Combination Sum - Unbounded backtracking
40. Combination Sum II - With duplicates handling
46. Permutations - Classic permutation generation
47. Permutations II - Permutations with duplicates
77. Combinations - Choose k from n
78. Subsets - Power set generation
79. Word Search - 2D grid backtracking
90. Subsets II - Subsets with duplicates
93. Restore IP Addresses - String partition backtracking
131. Palindrome Partitioning - Partition into palindromes
216. Combination Sum III - Fixed count combinations
254. Factor Combinations - Factor backtracking
526. Beautiful Arrangement - Permutation with constraint
784. Letter Case Permutation - Case combinations

Hard

37. Sudoku Solver - Constraint satisfaction
51. N-Queens - Classic backtracking problem
52. N-Queens II - Count solutions variant
212. Word Search II - Trie + backtracking on board
351. Android Unlock Patterns - Path validation backtracking
996. Number of Squareful Arrays - Permutation with constraints

Heap & Priority Queue

Easy

703. Kth Largest Element in Stream - Min heap of size k
1046. Last Stone Weight - Max heap simulation

Medium

215. Kth Largest Element in Array - Quickselect or heap
253. Meeting Rooms II - Min heap for intervals
347. Top K Frequent Elements - Heap or bucket sort
355. Design Twitter - Merge k sorted lists with heap
373. Find K Pairs with Smallest Sums - Min heap optimization
378. Kth Smallest Element in Sorted Matrix - Binary search or heap
621. Task Scheduler - Max heap with cooldown
658. Find K Closest Elements - Binary search + two pointers
692. Top K Frequent Words - Heap with custom comparator
767. Reorganize String - Max heap greedy placement
973. K Closest Points to Origin - Max heap or quickselect
1481. Least Number of Unique Integers - Min heap greedy

Hard

23. Merge k Sorted Lists - Min heap merge
295. Find Median from Data Stream - Two heaps (max + min)
352. Data Stream as Disjoint Intervals - Ordered map or heap
358. Rearrange String k Distance Apart - Max heap with queue
407. Trapping Rain Water II - Min heap with boundary
502. IPO - Two heaps greedy
632. Smallest Range Covering Elements - Min heap with pointers
778. Swim in Rising Water - Dijkstra with heap
857. Minimum Cost to Hire K Workers - Max heap optimization

Binary Search

Easy

35. Search Insert Position - Basic binary search
69. Sqrt(x) - Binary search on answer
278. First Bad Version - Find first occurrence
367. Valid Perfect Square - Binary search validation
374. Guess Number Higher or Lower - Interactive binary search
704. Binary Search - Standard implementation

Medium

33. Search in Rotated Sorted Array - Modified binary search
34. Find First and Last Position - Binary search bounds
74. Search 2D Matrix - Treat as 1D array
81. Search in Rotated Sorted Array II - With duplicates
153. Find Minimum in Rotated Sorted Array - Find pivot
154. Find Minimum in Rotated Sorted Array II - With duplicates
162. Find Peak Element - Binary search on unsorted
209. Minimum Size Subarray Sum - Binary search or sliding window
240. Search 2D Matrix II - Staircase search
275. H-Index II - Binary search on sorted
287. Find Duplicate Number - Binary search or Floyd's
300. Longest Increasing Subsequence - Binary search optimization
378. Kth Smallest in Sorted Matrix - Binary search on value range
436. Find Right Interval - Binary search with sorting
540. Single Element in Sorted Array - Binary search parity
658. Find K Closest Elements - Binary search window
875. Koko Eating Bananas - Binary search on answer
1011. Capacity to Ship Packages - Binary search optimization
1062. Longest Repeating Substring - Binary search + rolling hash

Hard

4. Median of Two Sorted Arrays - Binary search partition
410. Split Array Largest Sum - Binary search on answer
668. Kth Smallest Number in Multiplication Table - Binary search count
719. Find Kth Smallest Pair Distance - Binary search + two pointers
778. Swim in Rising Water - Binary search + BFS
1482. Minimum Days to Make Bouquets - Binary search on days

Intervals

Easy

252. Meeting Rooms - Check overlap after sorting

Medium

56. Merge Intervals - Classic interval merging
57. Insert Interval - Insert and merge
228. Summary Ranges - Group consecutive numbers
253. Meeting Rooms II - Min heap or sweep line
435. Non-overlapping Intervals - Greedy interval scheduling
452. Minimum Arrows to Burst Balloons - Interval overlap counting
495. Teemo Attacking - Merge overlapping durations
616. Add Bold Tag in String - Merge intervals in string
715. Range Module - Interval tree or sorted container
763. Partition Labels - Greedy interval partitioning
986. Interval List Intersections - Two pointer merge

Hard

218. The Skyline Problem - Sweep line with heap
352. Data Stream as Disjoint Intervals - Ordered map merge
759. Employee Free Time - Merge all then find gaps
850. Rectangle Area II - Coordinate compression

Greedy Algorithms

Easy

121. Best Time to Buy and Sell Stock - Track minimum
392. Is Subsequence - Greedy matching
455. Assign Cookies - Sort and match
860. Lemonade Change - Greedy change making

Medium

45. Jump Game II - Greedy BFS
55. Jump Game - Greedy reachability
122. Best Time to Buy and Sell Stock II - Capture all increases
134. Gas Station - One pass greedy
135. Candy - Two pass greedy
252. Meeting Rooms - Sort and check
253. Meeting Rooms II - Min heap greedy
334. Increasing Triplet - Track two minimums
406. Queue Reconstruction by Height - Sort and insert
435. Non-overlapping Intervals - Interval scheduling
452. Minimum Arrows to Burst Balloons - Interval overlap
621. Task Scheduler - Greedy with max frequency
646. Maximum Length of Pair Chain - Activity selection
649. Dota2 Senate - Queue greedy
763. Partition Labels - Track last occurrence
1007. Minimum Domino Rotations - Greedy check candidates

Hard

44. Wildcard Matching - Greedy or DP
135. Candy - Two pass greedy
358. Rearrange String k Distance Apart - Heap greedy
630. Course Schedule III - Max heap greedy
765. Couples Holding Hands - Cycle counting greedy
843. Guess the Word - Minimax greedy
968. Binary Tree Cameras - Greedy DFS

Bit Manipulation

Easy

136. Single Number - XOR all elements
190. Reverse Bits - Bit shifting
191. Number of 1 Bits - Count set bits
231. Power of Two - n & (n-1) == 0
268. Missing Number - XOR approach
338. Counting Bits - DP with bit manipulation
389. Find the Difference - XOR characters
461. Hamming Distance - Count XOR bits

Medium

29. Divide Two Integers - Bit shift division
78. Subsets - Bit masking for subsets
89. Gray Code - Bit manipulation pattern
137. Single Number II - Bit counting modulo
187. Repeated DNA Sequences - Bit encoding hash
201. Bitwise AND of Numbers Range - Find common prefix
260. Single Number III - XOR partition
318. Maximum Product of Word Lengths - Bit mask for characters
371. Sum of Two Integers - Add without + operator
477. Total Hamming Distance - Count bits per position
645. Set Mismatch - XOR technique
1318. Minimum Flips to Make OR Equal - Bit by bit comparison

Hard

52. N-Queens II - Bit masking backtracking
421. Maximum XOR of Two Numbers - Trie or greedy bit
864. Shortest Path to Get All Keys - BFS with bit state
982. Triples with Bitwise AND Equal To Zero - Hash map optimization
1178. Number of Valid Words for Puzzles - Bit masking with hash

Design Problems

Easy

155. Min Stack - Stack with min tracking
225. Implement Stack using Queues - Queue-based stack
232. Implement Queue using Stacks - Stack-based queue
705. Design HashSet - Hash table implementation
706. Design HashMap - Hash map from scratch

Medium

146. LRU Cache - Hash map + doubly linked list
208. Implement Trie - Prefix tree structure
211. Add and Search Word - Trie with wildcard
284. Peeking Iterator - Iterator wrapper
297. Serialize and Deserialize Binary Tree - Tree encoding
341. Flatten Nested List Iterator - Stack-based flattening
348. Design Tic-Tac-Toe - Optimized board checking
355. Design Twitter - Timeline with heap
359. Logger Rate Limiter - Hash map with timestamp
362. Design Hit Counter - Queue or circular buffer
380. Insert Delete GetRandom O(1) - Array + hash map
432. All O(1) Data Structure - Hash map + doubly linked list
460. LFU Cache - Complex hash map structure
535. Encode and Decode TinyURL - Hash-based encoding
588. Design In-Memory File System - Trie-based filesystem
622. Design Circular Queue - Array-based queue
641. Design Circular Deque - Double-ended queue
676. Implement Magic Dictionary - Trie with one char diff
706. Design HashMap - Custom hash implementation
716. Max Stack - Stack with max operations
1166. Design File System - Path-based hash map
1244. Design Leaderboard - Hash map + sorting
1352. Product of Last K Numbers - Prefix product

Hard

146. LRU Cache - O(1) all operations
295. Find Median from Data Stream - Two heaps design
297. Serialize and Deserialize Binary Tree - Tree codec
381. Insert Delete GetRandom O(1) - Duplicates - Hash map + array with duplicates
460. LFU Cache - Frequency-based eviction
588. Design In-Memory File System - Trie-based system
895. Maximum Frequency Stack - Nested hash maps

Recursion

Easy

21. Merge Two Sorted Lists - Recursive merge
70. Climbing Stairs - Basic recursion with memoization
104. Maximum Depth of Binary Tree - Simple tree recursion
206. Reverse Linked List - Recursive reversal
226. Invert Binary Tree - Tree transformation
509. Fibonacci Number - Classic recursion
700. Search in BST - BST recursion

Medium

17. Letter Combinations of Phone Number - Recursive backtracking
22. Generate Parentheses - Recursive generation
24. Swap Nodes in Pairs - Recursive swapping
50. Pow(x, n) - Fast exponentiation
77. Combinations - Recursive combinations
78. Subsets - Recursive subset generation
98. Validate Binary Search Tree - Recursive validation
114. Flatten Binary Tree to Linked List - Recursive flattening
143. Reorder List - Recursive approach
241. Different Ways to Add Parentheses - Divide and conquer
779. K-th Symbol in Grammar - Recursive pattern

Hard

25. Reverse Nodes in k-Group - Complex recursive reversal
84. Largest Rectangle in Histogram - Divide and conquer (or stack)
145. Binary Tree Postorder Traversal - Iterative using recursion concept
273. Integer to English Words - Recursive number conversion
282. Expression Add Operators - Recursive expression building
301. Remove Invalid Parentheses - BFS or recursive pruning

Sorting & Searching

Easy

35. Search Insert Position - Binary search insertion
88. Merge Sorted Array - Two pointer merge
167. Two Sum II - Binary search or two pointers
242. Valid Anagram - Sorting comparison
349. Intersection of Two Arrays - Set or sorting
350. Intersection of Two Arrays II - Two pointers after sort
704. Binary Search - Standard binary search
977. Squares of Sorted Array - Two pointer merge

Medium

33. Search in Rotated Sorted Array - Modified binary search
34. Find First and Last Position - Binary search bounds
56. Merge Intervals - Sort then merge
75. Sort Colors - Dutch national flag
147. Insertion Sort List - Sort linked list
148. Sort List - Merge sort O(n log n)
153. Find Minimum in Rotated Sorted Array - Binary search for minimum
162. Find Peak Element - Binary search peak
179. Largest Number - Custom comparator sorting
215. Kth Largest Element - Quickselect algorithm
240. Search 2D Matrix II - Staircase search
274. H-Index - Sorting with counting
324. Wiggle Sort II - Partition and interleave
347. Top K Frequent Elements - Bucket sort
451. Sort Characters By Frequency - Frequency sorting
912. Sort an Array - Implement sorting algorithms
973. K Closest Points - Quickselect or heap

Hard

4. Median of Two Sorted Arrays - Binary search partition
23. Merge k Sorted Lists - Divide and conquer merge
327. Count of Range Sum - Merge sort with counting
493. Reverse Pairs - Modified merge sort

Math & Geometry

Easy

7. Reverse Integer - Integer overflow handling
9. Palindrome Number - Number manipulation
13. Roman to Integer - Conversion logic
50. Pow(x, n) - Fast power
66. Plus One - Digit array manipulation
67. Add Binary - Binary arithmetic
69. Sqrt(x) - Binary search or Newton's method
171. Excel Sheet Column Number - Base 26 conversion
172. Factorial Trailing Zeroes - Count factors of 5
202. Happy Number - Cycle detection
204. Count Primes - Sieve of Eratosthenes
258. Add Digits - Digital root
263. Ugly Number - Factor checking
268. Missing Number - Math formula or XOR
326. Power of Three - Mathematical check
367. Valid Perfect Square - Binary search
412. Fizz Buzz - Modulo operations
441. Arranging Coins - Quadratic formula
504. Base 7 - Base conversion
628. Maximum Product of Three Numbers - Consider negatives

Medium

2. Add Two Numbers - Linked list arithmetic
8. String to Integer (atoi) - String parsing with overflow
12. Integer to Roman - Greedy conversion
29. Divide Two Integers - Bit manipulation division
43. Multiply Strings - String multiplication
48. Rotate Image - Matrix transformation
50. Pow(x, n) - Fast exponentiation
54. Spiral Matrix - Matrix traversal
59. Spiral Matrix II - Generate spiral
60. Permutation Sequence - Factorial number system
62. Unique Paths - Combinatorics or DP
73. Set Matrix Zeroes - In-place marking
149. Max Points on a Line - Slope calculation
166. Fraction to Recurring Decimal - Long division with hash map
168. Excel Sheet Column Title - Base 26 encoding
172. Factorial Trailing Zeroes - Count 5s in factors
179. Largest Number - Custom comparator
223. Rectangle Area - Overlap calculation
264. Ugly Number II - DP with three pointers
279. Perfect Squares - BFS or DP
343. Integer Break - Math optimization (prefer 3s)
365. Water and Jug Problem - GCD (Bézout's identity)
396. Rotate Function - Mathematical pattern
413. Arithmetic Slices - Count consecutive differences
462. Minimum Moves to Equal Array Elements II - Median minimizes distance
523. Continuous Subarray Sum - Modulo with hash map
537. Complex Number Multiplication - Complex arithmetic
592. Fraction Addition and Subtraction - LCM and GCD
633. Sum of Square Numbers - Two pointers
640. Solve the Equation - Linear equation parsing
779. K-th Symbol in Grammar - Recursive pattern
883. Projection Area of 3D Shapes - 3D geometry
914. X of a Kind in Deck of Cards - GCD of frequencies
1492. The kth Factor of n - Factor enumeration

Hard

65. Valid Number - String validation with states
149. Max Points on a Line - Geometry with precision
224. Basic Calculator - Expression evaluation
233. Number of Digit One - Digit DP
273. Integer to English Words - Recursive conversion
335. Self Crossing - Geometry analysis
537. Complex Number Multiplication - Arithmetic parsing
587. Erect the Fence - Convex hull (Graham scan)
829. Consecutive Numbers Sum - Number theory
850. Rectangle Area II - Sweep line algorithm
858. Mirror Reflection - GCD and geometry
891. Sum of Subsequence Widths - Combinatorics with sorting
1363. Largest Multiple of Three - Modulo arithmetic

Advanced Topics

Union Find (Disjoint Set)

128. Longest Consecutive Sequence - Union-find or hash set
200. Number of Islands - Connected components
261. Graph Valid Tree - Cycle detection
305. Number of Islands II - Online union-find
323. Number of Connected Components - Union-find application
547. Number of Provinces - Friend circles
684. Redundant Connection - Find cycle edge
685. Redundant Connection II - Directed graph variant
721. Accounts Merge - Union by email
737. Sentence Similarity II - Transitive closure
765. Couples Holding Hands - Cycle counting
803. Bricks Falling When Hit - Reverse union-find
827. Making A Large Island - Union-find with size
924. Minimize Malware Spread - Component analysis
928. Minimize Malware Spread II - Advanced union-find
959. Regions Cut By Slashes - Grid subdivision
990. Satisfiability of Equality Equations - Constraint satisfaction
1319. Number of Operations to Make Network Connected - Component counting

Segment Tree & Binary Indexed Tree (Fenwick Tree)

218. The Skyline Problem - Sweep line with segment tree
307. Range Sum Query - Mutable - Segment tree or BIT
308. Range Sum Query 2D - Mutable - 2D BIT
315. Count of Smaller Numbers After Self - Merge sort or BIT
327. Count of Range Sum - Merge sort approach
493. Reverse Pairs - Modified merge sort
699. Falling Squares - Coordinate compression
732. My Calendar III - Segment tree for intervals
850. Rectangle Area II - Coordinate compression
1157. Online Majority Element - Segment tree with voting
1326. Minimum Number of Taps - Greedy or segment tree
1353. Maximum Number of Events - Greedy with priority queue
1648. Sell Diminishing-Valued Colored Balls - Math with priority queue

Advanced Graph Algorithms

269. Alien Dictionary - Topological sort
310. Minimum Height Trees - Tree center finding
332. Reconstruct Itinerary - Eulerian path
399. Evaluate Division - Weighted graph DFS
743. Network Delay Time - Dijkstra's algorithm
753. Cracking the Safe - De Bruijn sequence
787. Cheapest Flights Within K Stops - Bellman-Ford variant
815. Bus Routes - BFS on graph of routes
847. Shortest Path Visiting All Nodes - BFS with bitmask
882. Reachable Nodes In Subdivided Graph - Dijkstra with edges
1192. Critical Connections - Tarjan's algorithm (bridges)
1334. Find the City - Floyd-Warshall
1514. Path with Maximum Probability - Modified Dijkstra
1631. Path With Minimum Effort - Binary search + BFS or Dijkstra
1976. Number of Ways to Arrive at Destination - Dijkstra with counting

String Algorithms

28. Find the Index of First Occurrence - KMP algorithm
214. Shortest Palindrome - KMP for palindrome
459. Repeated Substring Pattern - KMP or string manipulation
686. Repeated String Match - String matching
796. Rotate String - KMP or concatenation
1044. Longest Duplicate Substring - Rolling hash + binary search
1062. Longest Repeating Substring - Binary search + rolling hash
1316. Distinct Echo Substrings - Rolling hash

Monotonic Stack/Queue Advanced

84. Largest Rectangle in Histogram - Classic monotonic stack
85. Maximal Rectangle - Histogram approach
239. Sliding Window Maximum - Monotonic deque
316. Remove Duplicate Letters - Greedy with stack
402. Remove K Digits - Monotonic stack greedy
456. 132 Pattern - Stack with tracking
581. Shortest Unsorted Continuous Subarray - Stack or two pass
901. Online Stock Span - Monotonic stack
907. Sum of Subarray Minimums - Contribution technique
1019. Next Greater Node In Linked List - Stack on list
1063. Number of Valid Subarrays - Monotonic stack counting
1118. Number of Days in a Month - Date calculation
1856. Maximum Subarray Min-Product - Monotonic stack with prefix

Game Theory & Minimax

292. Nim Game - Mathematical game theory
294. Flip Game II - Game state DP
375. Guess Number Higher or Lower II - Minimax DP
464. Can I Win - Game state with bitmask
486. Predict the Winner - Minimax DP
877. Stone Game - Game theory DP
913. Cat and Mouse - Graph game theory
1140. Stone Game II - DP with game state
1406. Stone Game III - Suffix DP
1510. Stone Game IV - Game DP with squares
1563. Stone Game V - Interval DP game
1686. Stone Game VI - Greedy with sorting
1872. Stone Game VIII - Prefix sum DP

Study Strategy & Tips

Week-by-Week Plan (12 Weeks)

Weeks 1-2: Foundations

Arrays & Strings (Easy + Medium)
Two Pointers & Sliding Window
Hash Maps & Sets
Practice 3-5 problems daily

Weeks 3-4: Data Structures

Stack & Queue
Linked Lists
Trees & BST (Easy + Medium)
Practice 3-5 problems daily

Weeks 5-6: Algorithms

Binary Search
Sorting & Searching
DFS & BFS basics
Practice 4-6 problems daily

Weeks 7-8: Advanced Patterns

Dynamic Programming (Easy + Medium)
Backtracking
Greedy Algorithms
Practice 4-6 problems daily

Weeks 9-10: Complex Topics

Advanced DP (Hard)
Graphs (Medium + Hard)
Trie, Heap, Intervals
Practice 5-7 problems daily

Weeks 11-12: Mock Interviews & Review

Hard problems from all categories
System Design basics
Mock interviews (2-3 per week)
Review weak areas

Problem-Solving Framework

Understand - Clarify requirements, constraints, edge cases
Plan - Choose data structures and algorithms
Implement - Write clean, readable code
Test - Check edge cases and optimize
Analyze - Time and space complexity

Key Patterns to Master

Sliding Window
Two Pointers
Fast & Slow Pointers
Merge Intervals
Cyclic Sort
In-place Reversal
Tree BFS/DFS
Two Heaps
Subsets
Modified Binary Search
Top K Elements
K-way Merge
Topological Sort
0/1 Knapsack
Unbounded Knapsack

Interview Tips

Always clarify the problem first
Discuss your approach before coding
Write clean, modular code
Explain your thought process
Test with examples
Optimize when possible
Handle edge cases
Practice time management (45 min per problem)

Resources

LeetCode - Primary practice platform
NeetCode.io - Video explanations
Striver's SDE Sheet - Comprehensive list
Blind 75 - Essential problems
AlgoExpert - Structured learning
Cracking the Coding Interview - Book
Elements of Programming Interviews - Book

carefree-ladka/Google 2026 LeetCode Interview Preparation Guide.mdx

Google 2026 LeetCode Interview Preparation Guide

Table of Contents

Arrays & Strings

Easy

Medium

Hard

Two Pointers & Sliding Window

Easy

Medium

Hard

Hash Maps & Sets

Easy

Medium

Hard

Stack & Queue

Easy

Medium

Hard

Linked Lists

Easy

Medium

Hard

Trees & Binary Search Trees

Easy

Medium

Hard

Trie (Prefix Tree)

Easy

Medium

Hard

Graphs & BFS/DFS

Easy

Medium

Hard

Dynamic Programming

Easy

Medium

Hard

Backtracking

Easy

Medium

Hard

Heap & Priority Queue

Easy

Medium

Hard

Binary Search

Easy

Medium

Hard

Intervals

Easy

Medium

Hard

Greedy Algorithms

Easy

Medium

Hard

Bit Manipulation

Easy

Medium

Hard

Design Problems

Easy

Medium

Hard

Recursion

Easy

Medium

Hard

Sorting & Searching

Easy

Medium

Hard

Math & Geometry

Easy

Medium

Hard

Advanced Topics