func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long INF = LONG_LONG_MAX;   const long long NINF = LONG_LONG_MIN;   const long long mmod = 1000000007;   int32_t main() {     long long k;     cin >> k;     while (k-- > 0) {       long long n;       cin >> n;       string s, t;       cin >> s >> t;       vector<long long> cnt(26, 0);       for (long long i = 0; i < n; i++) {         cnt[s[i] -  a ]++;         cnt[t[i] -  a ]++;       }       bool found = true;       for (long long i = 0; i < 26; i++)         if (cnt[i] & 1) found = false;       if (found) {         vector<pair<long long, long long>> ans;         for (long long i = 0; i < n - 1; i++) {           if (s[i] != t[i]) {             bool f = false;             for (long long j = i + 1; j < n; j++) {               if (t[j] == t[i]) {                 swap(s[i], t[j]);                 f = true;                 ans.emplace_back(i + 1, j + 1);                 break;               }             }             if (!f) {               for (long long j = i + 1; j < n; j++) {                 if (s[j] == t[i]) {                   swap(s[j], t[j]);                   swap(s[i], t[j]);                   ans.emplace_back(j + 1, j + 1);                   ans.emplace_back(i + 1, j + 1);                   break;                 }               }             }           }         }         cout <<  YES  << endl;         cout << (long long)ans.size() << endl;         for (pair<long long, long long> x : ans)           cout << x.first <<     << x.second << endl;       } else {         cout <<  No  << endl;       }     }   }   