Leetcode1497- check whether array pairs can be divided by K - array - hash table - count

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Note：

1、 All the numbers in the array , All the k Perform a remainder operation , In this way, the question can be changed into whether the sum of two numbers is equal to k
2、 Just take the remainder and open an array to record , After each number is fetched, the corresponding number is
3、 Traverse half the array , Each judgment mod[i] == mod[k - i] that will do
4、 Last , Because it's possible that two people can get the remainder 0 The situation of , Judge 0 Position number is not 2 Multiple

The code is as follows ：

class Solution {
    
public:
    bool canArrange(vector<int>& arr, int k) {
    
        vector<int> mod(k);
        for(auto num: arr)
            mod[(num % k + k) % k] ++;
        for(int i = 1; i <= k / 2; i ++)
            if(mod[i] != mod[k - i])
                return false;
        
        return mod[0] % 2 == 0;

    }
};