Leetcode 1497. Check If Array Pairs Are Divisible by k (python)

题目

解法：

解析见注释

class Solution:
    def canArrange(self, arr: List[int], k: int) -> bool:
        # main idea: First, we only need to consider the remain of every numbers. Second, we find the match between remains and see if all teh remains can form a valid match pair
        count = collections.defaultdict(int)
        # only store the remain of each number divided by k
        for num in arr:
            count[num%k] += 1
        # if there is number with remain 0, then the number of 0 must be times of 2
        if 0 in count:
            if count[0]%2 != 0:
                return False
            # must delete the remain 0 element
            del count[0]
        
        # for the rest of the remains, the count of remain and count of k-remain must be equal
        for remain in count.keys():
            if count[remain] != count[k-remain]:
                return False
        return True