K倍区间

link

代码

#include<iostream>

using namespace std;

const int N = 100010;

int cnt[N];

int main(){
	int n, k;
	cin >> n >> k;
	long long ans = 0;
	long long sum = 0, x = 0;
	for(int i = 1; i <= n; i++){
		cin >> x;
		sum = (sum + x) % k;
		ans += cnt[sum]++;
	}
	cout << ans + cnt[0];
	return 0;
}