Submission #1801462

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Source Code Expand

#include <iostream>
#include <fstream>
#include <iomanip>
#include <math.h>
#include <limits.h>
#include <algorithm>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <string>
#include <string.h>
#include <sstream>
#include <ctime>

using namespace std;

#define eps 1e-12
#define pi 3.14159265358979323846
#define pb push_back
#define mp make_pair
#define st first
#define nd second
#define bgn begin
#define ll long long
#define ld long double
#define ull unsigned long long
#define ii pair<ll,ll>








const int N=1e5+10;
ll n,m,x,c[N],c2[N],mn,mx,res;






void solve()
{
	cin>>n>>m;
	for(int i=0;i<=m;i++)c[i]=0;
	for(int i=1;i<=n;i++)
	{
		cin>>x;
		c[x%m]++;
		c2[x]++;
	}
	res=(c[0]/2);
	if(m%2==0)res+=c[m/2]/2;
	for(int i=1,j=m-1;i*2<m;i++,j--)
	{
		mn=min(c[i],c[j]);
		res+=mn;
		c[i]-=mn;
		c[j]-=mn;
	}
	for(int i=1;i+4<N;i++)
	{
		if(i%m==0||(i%m)*2==m)continue;
		mn=min(c[i%m],c2[i]/2);
		res+=mn;
		c[i%m]-=mn;
	}
	cout<<res<<"\n";
}

int main()
{
	std::ios::sync_with_stdio(0);
	cin.tie(0);
#ifdef localProject
	freopen("in.txt","r",stdin);
#endif
	solve();
	return 0;
}

Submission Info

Judge Result