func_code_string: #include <bits/stdc++.h>   using namespace std;   long long int parent[26];   long long int find(long long int x) {     if (x == parent[x]) return x;     return parent[x] = find(parent[x]);   }   void merge(long long int x, long long int y) { parent[y] = x; }   signed main() {     long long int n;     cin >> n;     for (long long int i = 0; i < 26; i++) parent[i] = i;     string a, b;     cin >> a >> b;     vector<pair<char, char>> diff;     for (long long int i = 0; i < n; i++) {       long long int x = a[i] -  a , y = b[i] -  a ;       long long int u = find(x), v = find(y);       if (u != v) {         merge(u, v);         diff.push_back(make_pair(a[i], b[i]));       }     }     cout << diff.size() << endl;     for (auto x : diff) cout << x.first <<     << x.second << endl;   }   