Submission #993871

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Source Code Expand

#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <memory>
#include <complex>
#include <numeric>
#include <cstdio>
#include <iomanip>

#define REP(i,m,n) for(int i=int(m);i<int(n);i++)
#define EACH(i,c) for (auto &(i): c)
#define all(c) begin(c),end(c)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort(begin(c),end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())

#ifdef LOCAL
#define DEBUG(s) cout << (s) << endl
#define dump(x)  cerr << #x << " = " << (x) << endl
#define BR cout << endl;
#else
#define DEBUG(s) do{}while(0)
#define dump(x) do{}while(0)
#define BR 
#endif
using namespace std;

using UI = unsigned int;
using UL = unsigned long;
using LL = long long int;
using ULL = unsigned long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<LL>;
using VS = vector<string>;
using PII = pair<int,int>;
using VP = vector<PII>;

constexpr double EPS = 1e-10;
constexpr double PI  = acos(-1.0);

template<class T> inline T sqr(T x) {return x*x;}

int main() {
	int n, m;
	cin >> n >> m;
	VI x(n);
	REP(i,0,n) cin >> x[i];
	sort(all(x), [&](const int &a, const int &b){return a%m < b%m;});
	//for (const auto &i: x) cout << i << endl;
	VI nums(m), p(m);
	REP(i,0,n) {
		nums[x[i]%m]++;
		if (i < n - 1 && x[i] == x[i+1]) {
			nums[x[i]%m]++;
			p[x[i]%m]+=2;
			i++;
		}
	}
	/*
	cout << "---" << endl;
	for (const auto &i: nums) cout << i << endl;
	cout << "---" << endl;
	for (const auto &i: p) cout << i << endl;
	cout << "---" << endl;
	*/
	int cnt = 0;
	cnt += (nums[0]/2);
	//cout << cnt << endl;
	if (m % 2 == 0) cnt += (nums[m/2]/2);
	//cout << cnt << endl;
	REP(i,1,(m+1)/2) {
		int num = min(nums[i],nums[m-i]);
		cnt += num;
	//cout << "1 " << cnt << endl;
		nums[i] -= num;
		nums[m-1] -= num;
		cnt += (min(nums[i], p[i])/2);
	//cout << "2 " << cnt << endl;
		cnt += (min(nums[m-i], p[m-i])/2);
	//cout << "3 " << cnt << " " << m-i << endl;
	}
	cout << cnt << endl;
	/*
	auto it = begin(x);
	int cnt = 0;
	while (*it%5 == 0) {
		cnt++;
		it++;
	}
	cnt = (cnt%2)*2;
	auto rit = rend(x);
	while (it < rit) {

	}
	*/
	
	return 0;
}

Submission Info

Judge Result