Submission #1691286

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Source Code Expand

#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "iomanip"
#include "random"

using namespace std;

const long long int MOD = 1000000007;
const long double EPS = 0.00000001;
const long double PI = 3.1415926535897932384626433;

long long int N, M, K, H, W, L, R;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> N >> M;
	vector<int>num(100001);
	vector<int>mod(M);
	for (int i = 0; i < N; i++) {
		cin >> K;
		num[K]++;
	}
	int ans = 0;
	for (int i = 0; i <= 100000; i++) {
		ans += num[i] / 2;
		num[i] %= 2;
		mod[i%M] += num[i];
	}
	ans += mod[0] / 2;
	if (M % 2 == 0) {
		ans += mod[M / 2] / 2;
	}
	for (int i = 1; i < M / 2; i++) {
		ans += min(mod[i], mod[M - i]);
	}
	cout << ans << endl;
	return 0;
}

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