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,m;
    cin>>n>>m;
    int a[n];
    rep(i,0,n) {cin>>a[i];}
    sort(a,a+n);
    set<int> S;
    int cnt=0;
    int i=0, j=n-1;
    while(i<j) {
        if (a[i] + a[j] > m) {j--;}
        else if (a[i] + a[j] <= m) {
            S.insert(i);
            S.insert(j);
            cnt++;
            i++; j--;
        }
    }      
    cnt += (n - S.size());
    cout<<cnt<<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();
    }
}