BOJ 4641 - Doubles [C++]

문제

링크

풀이

#include <iostream>
#include <set>
using namespace std;
 
bool solve(void) {
  int n; cin >> n;
  if (n == -1) return false;
 
  set<int> s;
  while (n) {
    s.insert(n);
    cin >> n;
  }
 
  int ans = 0;
  for (int x : s) {
    if (s.count(x*2)) ans++;
  }
  cout << ans << "\n";
  return true;
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  while (solve());
  return 0;
}