A. Maximum Number of Pairs in Array (opens new window)

For each distinct number, count its frequency F, add A[0] by F//2, add A[1] by F%2.

DETAILS

def numberOfPairs(self, A: List[int]) -> List[int]:
        ans = [0, 0]
        C = collections.Counter(A)
        for a in C.keys():
            ans[0] += C[a] // 2
            ans[1] += C[a] % 2
        return ans

B. Max Sum of a Pair With Equal Sum of Digits (opens new window)

DETAILS

def maximumSum(self, A: List[int]) -> int:
        ans = collections.defaultdict(list)
        res = -1
        for a in A:
            curr = sum(map(int, list(str(a))))
            ans[curr].append(a)
            ans[curr] = sorted(ans[curr])[-2:]
        for a in ans.keys():
            if len(ans[a]) == 2:
                res = max(res, sum(ans[a]))
        return res

C. Query Kth Smallest Trimmed Number (opens new window)

Trim each number as requested, sorted the number according with their original index and get the certain one.

DETAILS

def smallestTrimmedNumbers(self, A: List[str], Q: List[List[int]]) -> List[int]:
        return [sorted((a[-d:], i) for i, a in enumerate(A))[r - 1][1] for r, d in Q]

D. Minimum Deletions to Make Array Divisible (opens new window)

Get the gcd d of D, sort array A and find the smallest number from A that divided by d.

DETAILS

def minOperations(self, A: List[int], D: List[int]) -> int:
        d = functools.reduce(lambda x, y: gcd(x, y), D)
        A.sort()
        for i in range(len(A)):
            if d % A[i] == 0:
                return i
        return -1