Submission #995434

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Source Code Expand

#include <iostream>
#include <sstream>
#include <vector>
#include <string>
#include <cstring>
#include <algorithm>
#include <queue>
#include <map>
#include <set>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define INF 1<<30
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> P;

int main() {
	int n, m;
	cin >> n >> m;

	vector<int> x(n);
	rep(i, n) cin >> x[i];

	vector<int> v[100005];
	rep(i, n) {
		v[ x[i] % m ].push_back(x[i]);
	}

	map<int, int> ma;
	rep(i, n) {
		ma[x[i]]++;
	}

	int ans = 0;
	REP(i, 1, (m / 2) + (m % 2 != 0)) {
		int j = m - i;

		set<int> a;
		rep(k, v[i].size()) a.insert(v[i][k]);

		int A = 0;
		each(it, a) {
			A += ma[*it] / 2;
		}

		set<int> b;
		rep(k, v[j].size()) b.insert(v[j][k]);

		int B = 0;
		each(it, b) {
			B += ma[*it] / 2;
		}

		int cnt = min(v[i].size(), v[j].size());
		ans += cnt;

		int da = v[i].size() - cnt;
		int db = v[j].size() - cnt;

		ans += min(da / 2, A);
		ans += min(db / 2, B);
	}

	if(m % 2 == 0) {
		int i = m / 2;
		set<int> a;
		rep(k, v[i].size()) a.insert(v[i][k]);

		each(it, a) {
			ans += ma[*it] / 2;
		}
	}

	ans += v[0].size() / 2;
	cout << ans << endl;

	return 0;
}

Submission Info

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