func_code_string: #include <bits/stdc++.h>   using namespace std;   const double PI = 2 * acos(0.0);   mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());   mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());   const string DIGITS =  0123456789 ;   const string ALPH =  abcdefghijklmnopqrstuvwxyz ;   template <class T0, class T1>   inline ostream &operator<<(ostream &out, pair<T0, T1> &a) {     return out <<  {  << a.first <<  ,   << a.second <<  } ;   }   template <class T0, class T1>   inline istream &operator>>(istream &in, pair<T0, T1> &a) {     return in >> a.first >> a.second;   }   template <class T0, class T1, class T2>   inline ostream &operator<<(ostream &out, tuple<T0, T1, T2> &a) {     return out <<  {  << get<0>(a) <<  ,   << get<1>(a) <<  ,   << get<2>(a)                <<  } ;   }   template <class T0, class T1, class T2, class T3>   inline ostream &operator<<(ostream &out, tuple<T0, T1, T2, T3> &a) {     return out <<  {  << get<0>(a) <<  ,   << get<1>(a) <<  ,   << get<2>(a)                <<  ,   << get<3>(a) <<  } ;   }   template <class T>   inline ostream &operator<<(ostream &out, vector<T> &a) {     out <<  [ ;     for (int i = 0; i < int(a.size()); ++i)       out << a[i] << vector<string>{ ,  ,  ]   }[i + 1 == a.size()];     return out;   }   void smain();   signed main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     cout << setprecision(12) << fixed;     smain();     return 0;   }   const int L = 20;   vector<int> ts;   int used[L];   int comp[L];   vector<int> verts[L];   set<int> g[L];   vector<int> rg[L];   void top_sort(int v) {     used[v] = 1;     for (int to : g[v]) {       if (used[to] == 0) {         top_sort(to);       }     }     ts.push_back(v);     used[v] = 2;   }   void inv_dfs(int v, int c) {     used[v] = 1;     comp[v] = c;     verts[c].push_back(v);     for (int to : rg[v]) {       if (used[to] == 0) {         inv_dfs(to, c);       }     }     used[v] = 2;   }   const int N = 20;   int mat[N][N];   int dp[1 << N];   int mg[N];   const int oo = 1e9 + 10;   int solve(set<int> &vr) {     int edges = 0;     for (int i = 0; i < int(N); ++i) {       mg[i] = 0;       for (int j = 0; j < int(N); ++j) {         edges += mat[i][j];         if (mat[i][j]) mg[i] += 1 << j;       }     }     for (int mask = 0; mask < int(1 << N); ++mask) {       dp[mask] = oo;     }     dp[0] = 0;     for (int mask = 0; mask < int(1 << N); ++mask) {       for (int i = 0; i < int(N); ++i)         if (!((mask >> i) & 1)) {           int nmask = mask + (1 << i);           int anti = ((1 << N) - 1) ^ nmask;           int ed = __builtin_popcount(mask & mg[i]);           dp[nmask] = min(dp[nmask], (dp[mask] + (ed != 0 && vr.count(i))));         }     }     return dp[(1 << N) - 1];   }   void smain() {     int t;     cin >> t;     while (t--) {       ts.clear();       for (int i = 0; i < int(L); ++i) {         comp[i] = 0;         verts[i].clear();         used[i] = 0;         rg[i].clear();         g[i].clear();       }       int n;       cin >> n;       string a, b;       cin >> a >> b;       for (int i = 0; i < int(n); ++i)         if (a[i] != b[i]) {           g[a[i] -  a ].insert(b[i] -  a );         }       vector<set<int>> t(L);       for (int i = 0; i < int(L); ++i) {         if (used[i]) continue;         top_sort(i);       }       reverse(ts.begin(), ts.end());       for (int v = 0; v < int(L); ++v) {         for (int to : g[v]) {           rg[to].push_back(v);         }         used[v] = 0;       }       int cnt = 0;       int ans = 0;       for (auto v : ts) {         if (used[v]) continue;         inv_dfs(v, cnt++);         if (verts[comp[v]].size() != 1) {           for (int i = 0; i < int(N); ++i) {             for (int j = 0; j < int(N); ++j) {               mat[i][j] = 0;             }           }           set<int> vr(verts[comp[v]].begin(), verts[comp[v]].end());           for (int v = 0; v < int(L); ++v) {             for (int to : g[v]) {               if (vr.count(v) && vr.count(to)) {                 mat[v][to] = 1;               }             }           }           ans += verts[comp[v]].size() - 1;           ans += solve(vr);         }       }       for (int v = 0; v < int(L); ++v) {         for (int to : g[v]) {           if (comp[v] != comp[to]) {             t[comp[v]].insert(comp[to]);           }         }       }       for (int i = 0; i < int(cnt); ++i) {         t[i].erase(i);         if (t[i].empty()) continue;         ans++;         t[*t[i].begin()].insert(t[i].begin(), t[i].end());       }       cout << ans <<   n ;     }   }   