Submission #996181

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Source Code Expand

#include<iostream>
#include<algorithm>
using namespace std;
int n,m,a[100000],c[100000],d[100000];
vector<int>b[100000];
int main(){
	cin>>n>>m;
	for(int i=0;i<n;i++){cin>>a[i];b[a[i]%m].push_back(a[i]);}
	for(int i=0;i<m;i++){
		sort(b[i].begin(),b[i].end());int v=1;
		for(int j=1;j<b[i].size();j++){
			if(b[i][j]!=b[i][j-1]){if(v%2==1)c[i]++;d[i]+=v/2;v=1;}
			else v++;
		}
		if(b[i].size()>=1){if(v%2==1)c[i]++;d[i]+=v/2;}
	}
	int cnt=0;
	for(int i=0;i<=m/2;i++){
		int t=(m-i)%m;
		if(i!=t){
			int F1=min(b[i].size(),b[t].size());
			int F2=F1;cnt+=F1;
			int G1=min(c[i],F1);F1-=G1;c[i]-=G1;if(F1>=1)d[i]-=(F1+1)/2;
			int G2=min(c[t],F2);F2-=G2;c[t]-=G2;if(F2>=1)d[t]-=(F2+1)/2;
		}
		if(i==t){cnt+=b[i].size()/2;c[i]=b[i].size()%2;d[i]=0;}
	}
	for(int i=0;i<m;i++)cnt+=d[i];
	cout<<cnt<<endl;
	return 0;
}

Submission Info

Judge Result