没有TLE，但是MLE，求指点

#include<iostream>
#include<queue>
#include<cstring>
using namespace std;
int table[401][401],n,m,x,y,v,xna,yna;
int stepx[]={1, 2 ,2,1,-1,-2,-2,-1},
    stepy[]={-2,-1,1,2,2 ,1 ,-1,-2};
struct Pos{
    int x,y,v;
};
queue<Pos> q;
Pos t,pos;
int main(){
    memset(table,-1,sizeof(table));
    cin>>n>>m>>x>>y;
    table[x][y]=0;
    pos.x = x;
    pos.y = y;
    pos.v = 0; 
    q.push(pos);
    while(q.empty()==0){
        pos = q.front();
        q.pop();
        if(table[pos.x][pos.y]==-1)table[pos.x][pos.y] = pos.v;
        for(int i=0;i<=7;i++){
            xna = pos.x+stepx[i];
            yna = pos.y+stepy[i];
            if((1<=xna && xna<=n)&&(yna>=1 &&yna<=m)){
                if(table[xna][yna]==-1){
                    t.x = xna;
                    t.y = yna;
                    t.v = pos.v + 1;
                    q.push(t);
                }
            }

        }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            cout<<table[i][j]<<' ';
        }   
        cout<<endl;
    }
    return 0;
}

最后就这样了 问题在哪里 求指导