Ferris Wheel

Solution

#include <bits/stdc++.h>
using namespace std;
//author: von_Braun
#define ll long long
#define lli long long int
#define pb push_back
#define rep(var, start, num) for(ulli var = start; var <start + num; var++)
#define all(x) x.begin(), x.end()
#define ulli unsigned long long int
#define ull unsigned long long
bool sortbysec(const pair<ll,ll> &a,const pair<ll,ll> &b) { return (a.second < b.second); }

void solve() {
    int n,x;
    cin>>n>>x;
    int ans=0;
    int k;
    multiset<int> S;
    rep(i,0,n) {cin>>k; S.insert(k);}
    while(S.size()>0) {
        auto start = S.begin();
        auto huh = S.upper_bound(x - *start);
        if (huh!=S.begin()) {huh--;
        if (huh!=S.begin()) {
        S.erase(huh);
        S.erase(S.begin());
        ans++;} else {
            ans++;
            S.erase(huh);
        } } else {
            ans++;
            S.erase(huh);
        }
    }
    cout<<ans<<endl;
}

int main() {
    //add quotes incase input output file
    //freopen(input.txt,r,stdin);
    //freopen(output.txt,w,stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int tc = 1;
    // cin >> tc;
    for (int t = 1; t <= tc; t++) {
        solve();
    }
}