func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n;     scanf( %d , &n);     char ar[n + 2];     char br[n + 2];     scanf( %s%s , ar + 1, br + 1);     vector<int> v[2];     for (int i = 1; i <= n; i++) {       if (ar[i] != br[i]) {         if (ar[i] ==  a )           v[0].push_back(i);         else           v[1].push_back(i);       }     }     if ((v[0].size() + v[1].size()) % 2 == 1)       cout << -1 << endl;     else {       int res = v[0].size() + v[1].size();       res /= 2;       if (v[0].size() % 2) res += 1;       cout << res << endl;       for (int i = 1; i < v[0].size(); i += 2) {         cout << v[0][i - 1] <<     << v[0][i] << endl;       }       for (int i = 1; i < v[1].size(); i += 2) {         cout << v[1][i - 1] <<     << v[1][i] << endl;       }       if (v[0].size() % 2) {         cout << v[0][v[0].size() - 1] <<     << v[0][v[0].size() - 1] << endl;         cout << v[0][v[0].size() - 1] <<     << v[1][v[1].size() - 1] << endl;       }     }     return 0;   }   