Shaddyjr

# source: https://www.hackerrank.com/challenges/sherlock-and-valid-string/problem
# video: https://youtu.be/WTwih7Ghvig
def isValid(s):
    count_of_chars = dict()
    
    for char in s:
        if char not in count_of_chars:
            count_of_chars[char] = 0
        count_of_chars[char] += 1
            

Shaddyjr

# source: https://www.hackerrank.com/challenges/beautiful-triplets/problem
# video: https://youtu.be/fOUWTyxYXUQ

def beautifulTriplets(d, arr):
    # Keep a running count dict
    counts = {}
    total = 0
    # loop through list to get counts
    for val in arr: # O(n)
        if val not in counts:

Shaddyjr

# source: https://www.hackerrank.com/challenges/equality-in-a-array/problem
# video: https://youtu.be/CLIVaqu39wU

def equalizeArray(arr):
    # keep dict of counts
    counts = {}
    # keep highest count item
    highest_count_item = arr[0]
    # loop through list to take counts
    for item in arr: # O(n)

Shaddyjr

# source: https://www.hackerrank.com/challenges/acm-icpc-team/problem
# video: https://youtu.be/tfHd30CGAWs

def acmTeam(topic):
    # keep track of teams (hashmap/dict)
    teams = {}
    length = len(topic)
    for i in range(length - 1): # O(n)
        curr_bin_string = topic[i] # first team member
        # Take each bit set and use OR operation to create combined topic knowledge team

Shaddyjr

# source: https://www.hackerrank.com/challenges/taum-and-bday/problem
# video: https://youtu.be/9vajRE0bJ5w

def taumBday(b, w, bc, wc, z):
    # if black gifts > white gifts + z conversion cost
    if bc > wc + z:
        return (w * wc) + (b * (wc + z))
    # if white gifts > black gifts + z conversion cost
    if wc > bc + z:
        return (b * bc) + (w * (bc + z))

Shaddyjr

def roadsAndLibraries(n, c_lib, c_road, cities):
    # if library cost is less than road cost, then cheaper to only build libraries
    if c_lib <= c_road:
        return n * c_lib
    
    city_groups = {city_id:{city_id} for city_id in range(1,n + 1)}
    # groups = {1: {1}, 2: {2}, 3: {3}, 4: {4}, 5: {5}}
    
    for city_a, city_b in cities: # O(m); where m = number of all city roads        
        city_groups[city_a].add(city_b)

Shaddyjr

# source: https://www.hackerrank.com/challenges/board-cutting/problem
def boardCutting(cost_y, cost_x):
    MOD_INT = (10**9) + 7
    
    # sort each cost (asc)
    cost_y.sort() # O(nlogn)
    cost_x.sort() # O(mlogm)
    
    horizontal_boards = 1
    vertical_boards   = 1

Shaddyjr

# source: https://www.hackerrank.com/challenges/hackerland-radio-transmitters

def hackerlandRadioTransmitters(houses, transmitter):
    houses.sort() # requires sorting => O(nlogn)
    transmitter_count = 0
    i = 0
    while i < len(houses): # O(n)
        transmitter_count += 1
        max_transmitting_house = houses[i] + transmitter
        # position after transmitting house

Shaddyjr

# source: https://www.hackerrank.com/challenges/3d-surface-area/problem
# video: https://youtu.be/tIG0GF2EqjE

def surfaceArea(A):
    n_rows = len(A)
    n_cols = len(A[0])
    total = (n_rows * n_cols) * 2 # top and bottom 
    for row_i in range(n_rows): # O(n)
        for col_i in range(n_cols): # O(m)
            val = A[row_i][col_i]

Shaddyjr

# source: https://leetcode.com/problems/combination-sum
# video: https://youtu.be/0Jt9_qKimCU

def combinationSum(candidates, target):
    dp = [[] for _ in range(target + 1)] # len(dp) = target + 1 b/c want to start with 0
    # intitialize with target = 0, must be empty
    dp[0].append([]) # start out as empty list, with sum total = 0

    # since combinations mean order doesn't matter, we should ensure we don't pass over 
    # parts already calculated ("old" ground)