func_code_string: #include <bits/stdc++.h>   using namespace std;   string a, b;   struct node {     int x, y;   };   vector<node> ans;   void rua() {     ans.clear();     int n;     scanf( %d , &n);     cin >> a >> b;     for (int i = 0; i < n; i++)       if (a[i] != b[i])         for (int j = i + 1; j < n; j++) {           if (a[i] == a[j]) {             swap(a[j], b[i]);             ans.push_back({j, i});             break;           }           if (a[i] == b[j]) {             swap(a[j], b[j]);             ans.push_back({j, j});             swap(a[j], b[i]);             ans.push_back({j, i});             break;           }         }     if (a != b) {       printf( NO n );       return;     }     printf( YES n%d n , (int)ans.size());     for (auto i : ans) printf( %d %d n , i.x + 1, i.y + 1);   }   int main() {     int t;     scanf( %d , &t);     while (t--) rua();     return 0;   }   