Submission #1608451

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Source Code Expand

#include <bits/stdc++.h>
#define REP(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
#define LL long long

using namespace std;

int main(){

    int N,M;cin>>N>>M;
    int X[N];REP(i,N)cin>>X[i];
    sort(X,X+N);

    int cnt[M];
    fill_n(cnt,M,0);
    int pr[M];
    fill_n(pr,M,0);

    REP(i,N)cnt[X[i]%M]++;
    REP(i,N)if(X[i]==X[i+1])pr[X[i++]%M]++;

    int ans=cnt[0]/2;
    for (int i=1;i<M;i++){
        int num = min(cnt[i],cnt[M-i]);
        if(i==M-i)num/=2;
        ans +=num;
        cnt[i]-=num;
        cnt[M-i]-=num;
    }
    for(int i=1;i<M;i++)ans += min(pr[i],cnt[i]/2);
    cout<<ans<<endl;


    return 0;
}

Submission Info

Judge Result