c++ bfs求最短路径长度

#include <bits/stdc++.h>
using namespace std;

typedef pair<int, int> PII;
#define fi first
#define se second

const int N=155;
int n, m;
char G[N][N];
int dist[N][N];
const int dirs[8][2]={{-2,-1}, {-2,1}, {-1,-2}, {-1,2}, {1,-2}, {1,2}, {2, -1}, {2, 1}};

int main(){
    memset(dist, -1, sizeof dist);
    memset(G, 0x00, sizeof G);
    cin>>m>>n;
    for(int i=0; i<n; ++i) cin>>G[i];

    int posx=-1, posy=-1;
    for(int i=0; i<n; ++i)
        for(int j=0; j<m; ++j)
            if(G[i][j]=='K') {posx=i, posy=j;}

    function<int(int, int)> bfs=[&](int posx, int posy){
        queue<PII> q;
        q.push({posx, posy});
        dist[posx][posy]=0;
        while(!q.empty()){
            int x=q.front().fi;
            int y=q.front().se;
            q.pop();
            for(int i=0; i<8; ++i){
                int nx=x+dirs[i][0];
                int ny=y+dirs[i][1];
                if(0<=nx&&nx<n&&0<=ny&&ny<m&&dist[nx][ny]==-1){
                    if(G[nx][ny]=='H') return dist[x][y]+1;
                    else{
                        q.push({nx, ny});
                        dist[nx][ny]=dist[x][y]+1;
                    }
                }
            }
        }
        return -1;
    };

    cout<<bfs(posx, posy)<<endl;


    return 0;
}