Submission #993121

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Source Code Expand

#include<iostream>
#include<vector>
#include<set>
using namespace std;

int main(){
  int n, m;
  std::cin >> n >> m;
  vector<int> x(n);
  for (int i = 0; i < n; i++) {
    std::cin >> x[i];
  }
  vector<int> mod(m, 0);
  for (int i = 0; i < n; i++) {
    mod[x[i]%m]++;
  }
  int ans = 0, tmp;

  for (int i = 1; i <= m/2; i++) {
    if(i == m - i)break;
    tmp = min(mod[i], mod[m - i]);
    ans += tmp;
    mod[i] -= tmp;
    mod[m - i] -= tmp;
  }
  if(m%2 == 0){
    tmp = mod[m/2]/2;
    ans += tmp;
    mod[m/2] -= tmp*2;
  }
  tmp = mod[0]/2;
  ans += tmp;
  mod[0] -= tmp*2;
  set<int> s;
  for (int i = 0; i < n; i++) {
    if(s.find(x[i]) != s.end() and mod[x[i]%m] >= 2){
      mod[x[i]%m] -= 2;
      ans++;
    }
    s.insert(x[i]);
  }
  std::cout << ans << std::endl;
  return 0;
}

Submission Info

Judge Result