fork download
copy 
  1. #include <iostream>
  2. #include <vector>
  3. #include <cmath>
  4.  
  5. using namespace std;
  6.  
  7. int main() {
  8.     int n;
  9.     if (!(cin >> n)) return 0;
  10.     vector<int> arr(n);
  11.     for (int i = 0; i < n; i++) {
  12.         cin >> arr[i];
  13.     }
  14.  
  15.     long long int target;
  16.     cin >> target;
  17.  
  18.     // Use long long to avoid integer overflow during multiplications
  19.     long long int c1 = 0;
  20.     long long int c2 = 0;
  21.     long long int c3 = 0;
  22.     long long int c4 = 0;
  23.  
  24.     // target must be non-negative and even
  25.     if (target >= 0 && target % 2 == 0) {
  26.         long long int k = target / 2;
  27.         for (int i = 0; i < n; i++) {
  28.             if (arr[i] == k) {
  29.                 c1++;
  30.             } else if (arr[i] == -k) {
  31.                 c2++;
  32.             } else if (arr[i] >= 0 && abs(arr[i]) < k) {
  33.                 c3++;
  34.             } else if (arr[i] < 0 && abs(arr[i]) < k) {
  35.                 c4++;
  36.             }
  37.         }
  38.     }
  39.  
  40.     long long int ans = 0;
  41.  
  42.     // Case A: Pairs where both elements have magnitude K
  43.     ans = ans + c1 * (c1 - 1) / 2; // (+K, +K)
  44.     ans = ans + c2 * (c2 - 1) / 2; // (-K, -K)
  45.     ans = ans + c1 * c2;           // (+K, -K)
  46.  
  47.     // Case B: Pairs where one element is +K and the other has smaller magnitude
  48.     ans = ans + c1 * c4;
  49.     ans = ans + c1 * c3;
  50.  
  51.     // Case C: Pairs where one element is -K and the other has smaller magnitude
  52.     ans = ans + c2 * c3;
  53.     ans = ans + c2 * c4;
  54.  
  55.     cout << ans << endl;
  56.  
  57.     return 0;
  58. }
Success #stdin #stdout 0s 5320KB
comments (?)
stdin
copy 
4
1 3 2 0
2
stdout
copy 
1
https://ideone.com/J2go8w
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!