Submission #992651

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Source Code Expand

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <iomanip>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
#define LONG_INF 1000000000000000
int wow[200000] = {};
int moduloed[200000] = {};
int used[200000] = {};
int main() {
	ios::sync_with_stdio(false);
	int n, m;
	cin >> n >> m;
	for (int i = 0;i < n;++i) {
		int tmp;
		cin >> tmp;
		wow[tmp%m]++;
		used[tmp]++;
	}
	for (int i = 0;i < 110000;++i) {
		moduloed[i%m] += used[i] / 2;
	}
	int ans = 0;
	for (int i = 1;i < m;++i) {
		int hoge = min(wow[i], wow[m - i]);
		ans += hoge;
		wow[i] -= hoge;
		wow[m-i] -= hoge;
		if (wow[i] != 0) {
			ans += min(wow[m - i],moduloed[m-i]) / 2;
		}
		else {
			ans += min(wow[i], moduloed[i]) / 2;
		}
	}
	ans += wow[0] / 2;
	cout << ans << endl;
	return 0;
}

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