Submission #995302

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

#define DUMP(x) cerr << #x << "=" << x << endl
#define DUMP2(x, y) cerr<<"("<<#x<<", "<<#y<<") = ("<<x<<", "<<y<<")"<< endl
#define BINARY(x) static_cast<bitset<16> >(x)

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define REP(i,m,n) for (int i=m;i<(int)(n);i++)

#define in_range(x, y, w, h) (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))
#define ALL(a) (a).begin(),(a).end()

typedef long long ll;
const int INF = 1e9;
typedef pair<int, int> PII;
int dx[4]={0, -1, 1, 0}, dy[4]={-1, 0, 0, 1};

int N, M;
const int MAX = 1e5 + 1;
int X[MAX], cnt[MAX], mod_cnt[MAX];

int num_same()
{
    int res = 0;
    rep(i, MAX) {
        res += cnt[i]/2;
    }
    // cerr << "num_same: " << res << endl;
    return res;
}

int num_mod()
{
    int res = 0;
    rep(i, M/2) {
        if (i == M-i) {
            res += mod_cnt[i]/2;
            mod_cnt[i] -= mod_cnt[i]/2;
        } else {
            int tmp = min(mod_cnt[i], mod_cnt[M-i]);
            mod_cnt[i] -= tmp;
            mod_cnt[M-i] -= tmp;
            res += tmp;
        }
    }
    // cerr << "num_mod: " << res/2 << endl;
    return res;
}
int main()
{
    ios::sync_with_stdio(false);

    cin >> N >> M;
    
    rep(i, N) {
        cin >> X[i];
        cnt[X[i]]++;
        mod_cnt[X[i] % M]++;
    }

    int ans = 0;
    ans += num_mod();
    ans += num_same();
    cout << ans << endl;
}

Submission Info

Judge Result