A. Minimum Number of Operations to Convert Time (opens new window)

Greedy Get time difference.

DETAILS

def convertTime(self, A: str, B: str) -> int:
        dif = (int(B[:2]) - int(A[:2])) * 60 + (int(B[3:]) - int(A[3:]))
        ans, dif = dif // 60, dif % 60
        ans, dif = ans + dif // 15, dif % 15
        ans, dif = ans + dif // 5, dif % 5
        return ans + dif

B. Find Players With Zero or One Losses (opens new window)

DETAILS

def findWinners(self, A: List[List[int]]) -> List[List[int]]:
        ppl = [0] * (10**5 + 1)
        lose = [0] * (10**5 + 1)
        for w, l in A:
            ppl[w] += 1
            ppl[l] += 1
            lose[l] += 1
        ans = [[], []]
        for i in range(10**5 + 1):
            if ppl[i] > 0 and lose[i] == 0:
                ans[0].append(i)
            if ppl[i] > 0 and lose[i] == 1:
                ans[1].append(i)
        return ans

C. Maximum Candies Allocated to K Children (opens new window)

Binary search: can we allocate k candies to each child?

DETAILS

def maximumCandies(self, A: List[int], ppl: int) -> int:
        l, r = 1, max(A)
        if sum(A) < ppl: return 0
        while l < r:
            m = (r + l + 1) // 2
            cur = 0
            for a in A:
                cur += a // m
            if cur >= ppl:
                l = m
            else:
                r = m - 1
        return l

D. Encrypt and Decrypt Strings (opens new window)

HashMap

DETAILS

class Encrypter:
    def __init__(self, K: List[str], V: List[str], D: List[str]):
        self.dict = set(D)
        self.trans = collections.defaultdict(str)
        self.back = collections.defaultdict(list)
        for pre, suf in zip(K, V):
            self.trans[pre] = suf
            self.back[suf].append(pre)
            
    def encrypt(self, word1: str) -> str:
        ans = ""
        for ch in word1:
            ans += self.trans[ch]
        return ans

    def decrypt(self, word2: str) -> int:
        ans = 0
        for word in self.dict:
            cur = ""
            valid = True
            for ch in word:
                if ch in self.trans:
                    cur += self.trans[ch]
                else:
                    valid = False
                    continue
            if valid:
                ans += int(cur == word2)
        return ans