func_code_string: #include <bits/stdc++.h>   using namespace std;   long long int gcd(long long int a, long long int b) {     if (a == 0) return b;     return gcd(b % a, a);   }   long long int INF = 1e17;   long long int NINF = (INF * -1);   priority_queue<pair<long long int, long long int>,                  vector<pair<long long int, long long int>>,                  greater<pair<long long int, long long int>>>       pq;   vector<long long int> indegree;   vector<vector<pair<long long int, long long int>>> adj;   vector<long long int> distances;   vector<vector<long long int>> arr;   vector<bool> visited;   vector<long long int> level, height;   vector<long long int> ans;   long long int dfs(long long int src, long long int parent = -1,                     long long int l = 0) {}   void solve() {     long long int n;     cin >> n;     string a;     string b;     cin >> a >> b;     vector<long long int> ab, ba;     vector<pair<long long int, long long int>> ans;     for (long long int i = 0; i < n; i++) {       if (a[i] == b[i]) {         continue;       }       if (a[i] ==  a  and b[i] ==  b ) {         if (ab.size() != 0) {           ans.push_back({ab.back(), i + 1});           ab.pop_back();         } else {           ab.push_back(i + 1);         }       } else {         if (ba.size() != 0) {           ans.push_back({ba.back(), i + 1});           ba.pop_back();         } else {           ba.push_back(i + 1);         }       }     }     if (ab.size() == 1 and ba.size() == 1) {       ans.push_back({ba.back(), ba.back()});       ans.push_back({ba.back(), ab.back()});       ab.pop_back();       ba.pop_back();     }     if (ab.size() != 0 || ba.size() != 0) {       cout <<  -1 n ;       return;     }     cout << ans.size();     cout <<   n ;     ;     for (auto i : ans) {       cout << i.first <<     << i.second;       cout <<   n ;       ;     }     return;   }   signed main() {     ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);     long long int t = 1;     while (t--) {       solve();     }   }   