Submission #3558241

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Source Code Expand

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define RG register
using namespace std;
const int N=1e5+10;
int n,m,num[N],ans,cnt[N],bck[N],cs[N],maxx[N];
inline int read(){
	char ch=getchar(); int x=0, f=1;
	while(ch<'0' || ch>'9'){if(ch=='-') f=-1; ch=getchar();	}
	while(ch>='0' && ch<='9'){x=x*10+ch-'0'; ch=getchar();	}
	return x*f;}
inline bool cmp(int a,int b){return a%m<b%m;}
inline int mx(int a,int b){return a>b ? a : b ;}
inline int mi(int a,int b){return a<b ? a : b ;}
int main()
{
//	freopen("Pair Cards.in","r",stdin);
	//freopen(".out","w",stdout);
	n=read(); m=read();
	for(int i=1;i<=n;i++) 
	{
		num[i]=read();//%m;
		cnt[num[i]%m]++;
		bck[num[i]]++;
	}
	ans+=cnt[0]/2;//printf("%d\n",ans);
	for(int i=1;i<m;i++)
	{
		if(i==m-i) 
		{
			ans+=cnt[i]/2;
			cnt[i]=1;
			continue;
		}
		int minn=mi(cnt[i],cnt[m-i]);
		ans+=minn;
		cnt[i]-=minn; cnt[m-i]-=minn;
	}
	for(int i=1;i<m;i++)
	{
		cnt[i]/=2;
		for(int j=i;j<=100000 && cnt[i]>0;j+=m)
		{
			ans+=mi(cnt[i], bck[j]/2);
			cnt[i]-=bck[j]/2;
		}
	}
	printf("%d\n",ans);
	//fclose(stdin); fclose(stdout);
	return 0;
}

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Judge Result