wayetan

/**
 * Given a binary tree

    struct TreeLinkNode {
      TreeLinkNode *left;
      TreeLinkNode *right;
      TreeLinkNode *next;
    }
    Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.
    

wayetan

/**
 * Given a binary tree, return the inorder traversal of its nodes' values.

    For example:
    Given binary tree {1,#,2,3},
       1
        \
         2
        /
       3

wayetan

/**
 * Given a binary tree, return the preorder traversal of its nodes' values.

    For example:
    Given binary tree {1,#,2,3},
       1
        \
         2
        /
       3

wayetan

/**
 * Given an array and a value, remove all instances of that value in place and return the new length.
 * The order of elements can be changed. It doesn't matter what you leave beyond the new length.
 */
 
 public class Solution {
    public int removeElement(int[] A, int elem) {
        int len = A.length;
        for(int i = 0; i < len; ){
            if(A[i] == elem)

wayetan

/**
 * You are climbing a stair case. It takes n steps to reach to the top.
 * Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
 */
 
public class Solution {
    public int climbStairs(int n) {
		int[] arr = new int[n + 1];
		arr[0] = 1;
		arr[1] = 1;

wayetan

/**
 * Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.
 * Do not allocate extra space for another array, you must do this in place with constant memory.
 * For example,
 * Given input array A = [1,1,2],
 * Your function should return length = 2, and A is now [1,2].
 */
 
public class Solution {
    public int removeDuplicates(int[] A) {

wayetan

/**
 * Find the contiguous subarray within an array (containing at least one number) which has the largest sum.
 * For example, given the array [−2,1,−3,4,−1,2,1,−5,4],
 * the contiguous subarray [4,−1,2,1] has the largest sum = 6.
 */
public class Solution {
    public int maxSubArray(int[] A) {
        int res = A[0], sum = 0;
        for(int i = 0; i < A.length; ++i){
            sum = Math.max(sum + A[i], A[i]);

wayetan

/**
 * Given a roman numeral, convert it to an integer.
 * Input is guaranteed to be within the range from 1 to 3999.
 */

public class Solution {
    public int romanToInt(String s) {
        HashMap<Character, Integer> dic = new HashMap<Character, Integer>();
        dic.put('I', 1);
        dic.put('V', 5);

wayetan

/**
 * Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
 * For example, this binary tree is symmetric:
 *     1
       / \
      2   2
     / \ / \
    3  4 4  3
 * But the following is not:
        1

wayetan

/**
 * Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
 */
 /**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;