func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     long long t;     cin >> t;     while (t--) {       long long n;       cin >> n;       vector<pair<long long, long long> > v(n);       for (long long i = 0; i < n; i++) {         cin >> v[i].first >> v[i].second;       }       sort(v.begin(), v.end());       long long a, b;       a = v[n - 1].first;       for (long long i = 0; i < n; i++) swap(v[i].first, v[i].second);       sort(v.begin(), v.end());       b = v[0].first;       if (a - b <= 0)         cout << 0 << endl;       else         cout << a - b << endl;     }     return 0;   }   