码风和宏定义比较唐，而且 0-index 。
大概是求距离的时候错了？但是一直找不到问题。

代码：

#include <bits/stdc++.h>
using namespace std;
random_device rd;
mt19937_64 rnd(rd());
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<db, db> pbb;
typedef pair<ld, ld> pdd;
typedef vector<int> vi;
typedef vector<ll> vl;
#define rep(i, a, b) for(int i = a; i <= b; i++)
#define per(i, a, b) for(int i = a; i >= b; i--)
#define sz(x) int(x.size())
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define eb emplace_back
#define pb push_back
#define MP make_pair
#define fi first
#define se second
#define YES(...) cout << "YES\n"
#define NO(...) cout << "NO\n"
template<typename T> void chkmin(T &a, const T &b){
  if(a > b) a = b;
}
template<typename T> void chkmax(T &a, const T &b){
  if(a < b) a = b;
}
const int R = 50, N = 15;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, -1, 0, 1};
int r, c, n;
char grid[R][R];
int idx[R][R], tot;
int g[N][N], d[R][R];
void bfs(int sx, int sy){
  queue<pii> q;
  q.push(MP(sx, sy));
  while(!q.empty()){
    pii p = q.front(); q.pop();
    for(int i = 0; i < 4; i++){
      int nx = p.fi + dx[i];
      int ny = p.se + dy[i];
      if(nx < 0 || nx >= r || ny < 0 || ny >= c) continue;
      if(~idx[nx][ny]) continue;
      if(grid[nx][ny] == 'S' || grid[nx][ny] == '.') continue;
      idx[nx][ny] = idx[sx][sy];
      q.push(MP(nx, ny));
    }
  }
}
void pathfind(int sx, int sy){
  memset(d, 0x3f, sizeof(d));
  queue<pii> q;
  q.push(MP(sx, sy));
  d[sx][sy] = 0;
  while(!q.empty()){
    pii p = q.front(); q.pop();
    for(int i = 0; i < 4; i++){
      int nx = p.fi + dx[i];
      int ny = p.se + dy[i];
      if(nx < 0 || nx >= r || ny < 0 || ny >= c || d[nx][ny] < 1E9) continue;
      d[nx][ny] = d[p.fi][p.se] + 1;
      q.push(MP(nx, ny));
    }
  }
  /*for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      cerr << d[i][j] << " \n"[j == c - 1];
    }
  }*/
  for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      if(grid[i][j] == 'X'){
        chkmin(g[idx[sx][sy]][idx[i][j]], d[i][j] - 1);
      }
    }
  }
}
int dp[1 << N][N];
signed main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  memset(dp, 0x3f, sizeof(dp));
  memset(g, 0x3f, sizeof(g));
  memset(idx, -1, sizeof(idx));
  cin >> r >> c;
  for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      cin >> grid[i][j];
    }
  }
  for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      if(grid[i][j] == 'X' && !~idx[i][j]){
        idx[i][j] = tot++;
        bfs(i, j);
      }
    }
  }
  /*for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      cerr << idx[i][j] << " \n"[j == c - 1];
    }
  }*/
  for(int i = 0; i < r; i++){
    for(int j = 0; j < c; j++){
      if(grid[i][j] == 'X'){
        pathfind(i, j);
      }
    }
  }
  // cerr << "tot: " << tot << '\n';
  /*for(int i = 0; i < tot; i++){
    for(int j = 0; j < tot; j++){
      cerr << g[i][j] << " \n"[j == tot - 1];
    }
  }*/
  for(int i = 0; i < tot; i++) g[i][i] = 0;
  for(int i = 0; i < tot; i++){
    dp[1 << i][i] = 0;
  }
  for(int S = 0; S < (1 << tot); S++){
    for(int u = 0; u < tot; u++){
      if(dp[S][u] >= 1E9) continue;
      if(!(S >> u & 1)) continue;
      for(int v = 0; v < tot; v++){
        if(S >> v & 1) continue;
        chkmin(dp[S | 1 << v][v], dp[S][u] + g[u][v]);
      }
    }
  }
  int ans = 1E9;
  for(int i = 0; i < tot; i++){
    chkmin(ans, dp[(1 << tot) - 1][i]);
  }
  cout << ans << '\n';
  return 0;
}