dobri

#include <bits/stdc++.h>
#define ll long long
#define INF 999999999
#define LINF 999999999999999999LL
#define N (1<<17)
#define M 1000000007

using namespace std;

unordered_map<int, bool> m;
int v[5000];

int main () {
  int n;
  cin>>n;
  int ans = 0;
  for (int i = 0; i < n; i++) {
    cin>>v[i];
    for (int j = 0; j < i; j++) {
      if (m[v[i] - v[j]]) {
	ans++;
	break;
      }
    }
    for (int j = 0; j <= i; j++) {
      m[v[i] + v[j]] = true;
    }
  }
  cout<<ans<<endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED