Submission #992889

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)

using ll = long long;
using P = std::tuple<int,int>;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

int cnt[100100];

vector<int> v[100000];

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

    int N, M;
    std::cin >> N >> M;

    for(int i=0;i<N;++i){
        int X;
        std::cin >> X;

        ++cnt[X];
    }

    for(int i=1;i<=100000;++i){
        for(int j=0;j<(cnt[i]&1);++j){
            v[i % M].emplace_back(i);
        }
    }

    for(int i=1;i<=100000;++i){
        for(int j=0;j<cnt[i]-(cnt[i]&1);++j){
            v[i % M].emplace_back(i);
        }
    }

    int res = 0;
    for(int i=0;i<M;++i){
        int i2 = (M - i) % M, v_size = v[i].size();
        if(i2 < i){break;}
        if(i == i2){
            for(int j=0;j<v_size-(v_size&1);j+=2){
                ++res;
                --cnt[v[i][j]];
                --cnt[v[i][j+1]];
                // std::cout << "double: " << v[i][j] << ", " << v[i][j+1] << std::endl;
            }
        }else{
            int mn = min(v[i].size(), v[i2].size());
            for(int j=0;j<mn;++j){
                ++res;
                --cnt[v[i][j]];
                --cnt[v[i2][j]];
                // std::cout << "single: " << v[i][j] << ", " << v[i2][j] << std::endl;
            }
        }
    }

    for(int i=1;i<=100000;++i){
        res += cnt[i] / 2;
    }

    std::cout << res << std::endl;
}

Submission Info

Judge Result