P171SUMB – ptit

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
const ll mod=1000000007;
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
int n, k, i, j, a[200004], cnt[500], ans;
int main() {
    cin >> n >> k;
    for (int i=1; i<=n; i++) cin >> a[i];
    for (int i=1; i<=n; i++) {
        a[i] = a[i] % k;
        ++cnt[a[i]];
    }
    for (int i=1; i<=k/2; i++) {
        ans = ans + max(cnt[i], cnt[k-i]);
    }
    if (k%2 == 0) {
        ans -= cnt[k/2];
        if (cnt[k/2]>0) ans++;
    }
    if (cnt[0] > 0) ans++;
    cout << ans;
	return 0;
}

#include <bits/stdc++.h> using namespace std; #define pb push_back #define mp make_pair #define all(x) (x).begin(),(x).end() #define fi first #define se second #define SZ(x) ((int)(x).size()) typedef vector<int> VI; typedef long long ll; typedef pair<int,int> PII; const ll mod=1000000007; ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;} int n, k, i, j, a[200004], cnt[500], ans; int main() { cin >> n >> k; for (int i=1; i<=n; i++) cin >> a[i]; for (int i=1; i<=n; i++) { a[i] = a[i] % k; ++cnt[a[i]]; } for (int i=1; i<=k/2; i++) { ans = ans + max(cnt[i], cnt[k-i]); } if (k%2 == 0) { ans -= cnt[k/2]; if (cnt[k/2]>0) ans++; } if (cnt[0] > 0) ans++; cout << ans; return 0; }