Submission #1484393

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<n;i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

constexpr int max_n = 100005;

int N,M;
vector<int> X;

int main(){
    cin >> N >> M;
    X.resize(N);
    vector<int> modcnt(M+10,0);
    vector<int> cnt(max_n,0);
    vector<int> rem(M+10,0);
    rep(i,N){
        cin >> X[i];
        modcnt[X[i]%M]++;
        cnt[X[i]]++;
    }

    int ans = 0;
    for(int i=0;i<=M/2;i++){
        int a = i;
        int b = (M - a)%M;
        //cerr << a << " " << b << endl;
        if(a==b){
            ans += modcnt[a]/2;
            rem[a] = modcnt[a]%2;
            continue;
        }

        int c = min(modcnt[a],modcnt[b]);
        rem[a] = modcnt[a]-c;
        rem[b] = modcnt[b]-c;
        ans += c;
    }
    //cerr << modcnt << endl;
    //cerr << rem << endl;
    //cerr << "ans :  " << ans << endl;

    for(int i=0;i<M;i++){
        int r = rem[i];
        int sum = 0;
        //cerr << "i : " << i << endl;
        //cerr << "r : " << r << endl;
        for(int v = i;v < max_n; v+=M){
            //cerr << "\tv : " << v << endl;
            int p = min(r/2,cnt[v]/2);
            sum += p;
            r -= p*2;
            if(r == 0 or r == 1) break;
        }
        ans += sum;
    }
    cout << ans << endl;
    return 0;
}

Submission Info

Judge Result