Submission #993454

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Source Code Expand

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

int main(){
  int n, m, maxi = 0;
  std::cin >> n >> m;
  vector<int> x(n);
  for (int i = 0; i < n; i++) {
    std::cin >> x[i];
    maxi = max(maxi, 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; 2*i <= m; i++) {
    if(2*i == m){
      tmp = mod[m/2]/2;
      ans += tmp;
      mod[m/2] -= tmp*2;
    }else{
      tmp = min(mod[i], mod[m - i]);
      ans += tmp;
      mod[i] -= tmp;
      mod[m - i] -= tmp;
    }
  }
  tmp = mod[0]/2;
  ans += tmp;
  mod[0] -= tmp*2;
  vector<int> s(maxi, 0);
  for (int i = 0; i < n; i++) {
    s[x[i]]++;
    if(s[x[i]] >= 2 and mod[x[i]%m] >= 2){
      s[x[i]] -= 2;
      mod[x[i]%m] -= 2;
      ans++;
    }
  }
  std::cout << ans << std::endl;
  return 0;
}

Submission Info

Judge Result