[BOJ] 14585 : 사수빈탕

#include <cstdio>
typedef long long ll;
int n, m, x;
ll r, s, a[1002]={1};
int main() {
    scanf("%d %d", &n, &m);
    while (n--) scanf("%d", &x), a[s=(s+x)%m]++;
    while (m--) r+=(a[m]*(a[m]-1))/2;
    printf("%lld", r);
    return 0;
}