1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> a(n);
	for (int& x : a) {
		cin >> x;
	}
	vector<int> sums;
	for (int i = 0; i < n; i++) {
		int s = 0;
		for (int j = i; j < n; j++) {
			s += a[j];
			sums.push_back(s);
		}
	}
	assert((int) sums.size() == n * (n + 1) / 2);
	long long answer = 0;
	int pref = 0;
	// map<int,int> mapka;
	const int MAGIC = 2 * 500 * 20'000;
	vector<int> cnt(2*MAGIC+1);
	for (int i = -1; i < n; i++) {
		if (i != -1) {
			pref += a[i];
		}
		for (int x : sums) {
			answer += cnt[-(pref+x)+MAGIC];
		}
		for (int x : sums) {
			cnt[x-pref+MAGIC]++;
		}
	}
	map<int,int> mapka;
	// mapka.clear();
	for (int x : sums) {
		answer -= mapka[-2*x] * 3;
		if (x % 2 == 0) answer -= mapka[-x/2] * 3;
		mapka[x]++;
	}
	for (int x : sums) {
		if (x == 0) {
			answer--;
		}
	}
	assert(answer % 6 == 0);
	cout << answer / 6 << endl;
}