DMOPC '20 Contest 4 P1 - Missing Numbers

    1#include <bits/stdc++.h>
    2 
    3using namespace std;
    4typedef long long ll;
    5int main(){
    6    ios::sync_with_stdio(0);
    7    cin.tie(0);
    8    int t;
    9    cin >> t;
    10    while(t--){
    11        ll n;
    12        ll s;
    13        cin >> n >> s;
    14        ll sum = n * (n + 1) / 2;
    15        ll diff = sum - s;
    16        if(diff < 3 || diff >= 2 * n){
    17            cout << 0 << '\n';
    18            continue;
    19        }
    20        ll low = max(1LL, diff - n);
    21        ll high = (diff - 1) / 2;
    22        cout << high - low + 1 << '\n';
    23    }
    24    return 0;
    25}