func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 20;   const int M = 1e5 + 55;   pair<int, int> dp[(1 << N) + 5];   int dis[N][N];   int My[(1 << N) + 5][N];   int taken[(1 << N) + 5][N];   char s[M];   int sum[N];   int lg[(1 << N) + 55];   int m, n;   pair<int, int> bt(int mask) {     if (mask == (1 << n) - 1) return {0, 0};     pair<int, int>& ret = dp[mask];     if (ret.first != -1) return ret;     ret = {10000000, 0};     int cur = 0;     pair<int, int> nxt;     for (int v = 0; v < n; v++) {       if ((mask & (1 << v)) == 0) {         nxt = bt(mask + (1 << v));         cur = nxt.second - My[mask][v];         cur += nxt.first + taken[mask][v];         if (cur < ret.first)           ret = {cur, nxt.second + taken[mask][v] - My[mask][v]};       }     }     return ret;   }   void prep(int mask, int i, int l, int pre) {     if (i == n - 1) {       taken[mask][l] = pre;       My[mask][l] = 0;       return;     }     if (My[mask][l] != -1) return;     for (int j = 0; j < n; j++) {       if ((mask & (1 << j)) == 0 && j != l) {         prep(mask + (1 << j), i + 1, l, pre + dis[l][j]);         My[mask][l] = My[mask + (1 << j)][l] + dis[l][j];       }     }     taken[mask][l] = pre;   }   int main() {     memset(dp, -1, sizeof dp);     memset(My, -1, sizeof My);     scanf( %d %d , &m, &n);     scanf( %s , s);     for (int i = 0; i < m - 1; i++) {       if (s[i] != s[i + 1]) {         dis[s[i] -  a ][s[i + 1] -  a ]++;         sum[s[i] -  a ]++;         sum[s[i + 1] -  a ]++;         dis[s[i + 1] -  a ][s[i] -  a ]++;       }     }     for (int i = 0; i < n; i++) lg[(1 << i)] = i;     int ms;     for (int l = 0; l < n; l++) {       for (int mask = (1 << n) - 1; mask >= 0; mask--) {         if (mask & (1 << l)) continue;         mask += (1 << l);         ms = mask | (mask + 1);         mask -= (1 << l);         ms -= (1 << l);         if (ms >= (1 << n)) {           taken[mask][l] = sum[l];           My[mask][l] = 0;           continue;         }         My[mask][l] = My[ms][l] + dis[lg[mask ^ ms]][l];         taken[mask][l] = taken[ms][l] - dis[l][lg[mask ^ ms]];       }     }     cout << bt(0).first << endl;     return 0;   }   