STL转模拟队列，30pts没看出来哪里错

#include <bits/stdc++.h>
using namespace std;
const int N = 410;
struct point{
    int x,y,step;
}que[N];
int n,m,sx,sy;
int ditu[N][N],vis[N][N];
int dir[8][2] = {{-2,-1},{-2,1},{-1,-2},{-1,2},{1,-2},{1,2},{2,-1},{2,1}};
void bfs(int x,int y) {
    int head = 0,tail = 1;
    ditu[x][y] = 0;
    vis[x][y] = 1;
    que[1] = {x,y,0};
    while(head < tail) {
        head++;
        for(int i = 0;i < 8;i++) {
            int nx = que[head].x + dir[i][0],ny = que[head].y + dir[i][1];
            if(nx >= 1 && ny >= 1 && nx <= n && ny <= m && !vis[nx][ny]) {
                tail++;
                vis[nx][ny] = 1;
                que[tail] = {nx,ny,que[head].step + 1};
                ditu[nx][ny] = que[tail].step;
            }
        }
    }

}


int main(){
    cin >> n >> m >> sx >> sy;
    memset(ditu,-1,sizeof(ditu));

    bfs(sx,sy);

    for(int i = 1;i <= n;i++) {
        for(int j = 1;j <= m;j++) {
            printf("%-5d",ditu[i][j]);
        }
        cout << endl;
    }
    return 0;
}