Submission #7562391

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i,l,r) for(int i=(int)(l);i<(int)(r);i++)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)x.size())
template<class T>bool chmax(T &a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a,T b){if(a>b){a=b;return 1;}return 0;}

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;

const int inf = 1LL<<60;
const int mod = 1e9 + 7;
const double eps = 1e-9;

/*{
  }*/

signed main(){
  int n, m;
  cin >> n >> m;

  vi a(n);
  rep(i, 0, n) cin >> a[i];

  vi cnt(100001);
  rep(i, 0, n){
    cnt[a[i]]++;
  }

  vi cnt1(m+1), cnt2(m+1);
  rep(i, 0, 100001){
    cnt1[i%m] += cnt[i]%2;
    cnt2[i%m] += cnt[i]/2;
  }

//  for(int i : cnt1) cout << i << " ";
//  cout << endl;
//  for(int i : cnt2) cout << i << " ";
//  cout << endl;

  int ans = 0;
  rep(i, 0, m){
    int t = min(cnt1[i], cnt1[m-i]);
    cnt1[i] -= t;
    cnt1[m-i] -= t;
    ans += t;
  }
  rep(i, 0, m){
    int t = min(cnt1[i]/2, cnt2[m-i]);
    cnt2[m-i] -= t;
    ans += 2*t;
  }
  rep(i, 0, m){
    ans += cnt2[i];
  }

  cout << ans << endl;

//  for(int i : cnt1) cout << i << " ";
//  cout << endl;
//  for(int i : cnt2) cout << i << " ";
//  cout << endl;

  return 0;
}

Submission Info

Judge Result