2518 和为S

动态维护hash即可
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<vector>
#include<cstring>
#include<stack>
#include <cmath>

#define mem(ss) memset(ss,0,sizeof(ss))
#define rep(d, s, t) for(int d=s;d<=t;d++)
#define rev(d, s, t) for(int d=s;d>=t;d--)
#define inf 0x3f3f3f3f
typedef long long ll;
typedef long double ld;
typedef double db;
typedef std::pair<int, int> pii;
typedef std::pair<ll, ll> pll;
const ll mod = 1e9 + 7;
const int N = 5e4 + 10;
#define io_opt ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
using namespace std;

ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }

int n, a[N] = {0}, s, ans = 0;
std::map<int, int> mp;

int main() {
    io_opt;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i], a[i] += a[i - 1];
    cin >> s;
    for (int i = 0; i < n; i++) {
        ++mp[a[i] + s];
        ans += mp[a[i+1]];
    }
    cout << ans;
    return 0;
}