Submission #992062

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Source Code Expand

#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define reps(X,S,Y) for (int (X) = S;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y)-1;(X) >=0;--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> using vv=vector<vector<T>>;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
const ll MOD=1e9+7;

int same(vector<int> &v){
  unordered_map<int,int> cnt;
  int re=0;
  for(int x:v) ++cnt[x];
  for(pii p:cnt) re+=p.Y/2;
  return re;
}

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int n,m;
  cin>>n>>m;
  vector<int> a(n);
  rep(i,n) cin>>a[i];
  vv<int> vs(m);
  for(int x:a) vs[x%m].pb(x);
  int re=vs[0].size()/2;
  //cout<<vs[0]<<endl;
  reps(i,1,m){
    if(m-i<=i) break;
    vector<int> &v=vs[i];
    vector<int> &w=vs[m-i];
    //cout<<v<<w<<same(w)<<endl;
    if(v.size()>w.size()) swap(v,w);
    re+=v.size()+max<int>((w.size()-v.size())/2,same(w));
  }
  if(m%2){
    //cout<<vs[m/2]<<endl;
    re+=vs[m/2].size()/2;
  }
  cout<<re<<endl;
  return 0;
}

Submission Info

Judge Result