多次BFS

#include <bits/stdc++.h>
using namespace std;
const int N = 310;
char g[N][N];
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
bool st[N][N];

int main()
{
    int n, m;
    while (cin >> n >> m, n && m) {
        memset(st, 0, sizeof st);
        pair<int,int> beg, ed;
        for (int i = 0 ; i < n ; i ++ ) {
            for (int j = 0 ; j < m ; j ++ ) {
                cin >> g[i][j];
                if (g[i][j] == '@') beg = {i, j};
                if (g[i][j] == '*') ed = {i, j};
            }
        }
        queue<pair<int,int>> q;
        q.push(beg);
        int ans = 0;
        st[beg.first][beg.second] = true;
        bool f = false;
        while (q.size()) {
            int l = q.size();
            for (int i = 0 ; i < l ; i ++ ) {
                auto t = q.front();
                if (t == ed) {
                    f = true;
                    break;
                }
                q.pop();
                for (int j = 0 ; j < 4 ; j ++ ) {
                    int x = t.first + dx[j];
                    int y = t.second + dy[j];
                    if (x >= 0 && x < n && y >= 0 && y < m && !st[x][y] && g[x][y] != '#') {
                        q.push({x, y});
                        st[x][y] = true;
                    }
                }
            }
            if (f) break;
            ans ++ ;
        }
        if (f) cout << ans << endl;
        else cout << -1 << endl;
    }
    return 0;
}