求助，为什么输出一堆-1

#include<bits/stdc++.h>
using namespace std;
int mp[505][505],p[505][505]={0};
int dx[8]={-2,-2,-1,-1,1,1,2,2};
int dy[8]={-1,1,-2,2,-2,2,-1,1};
int n,m,x,y;
struct node{
	int nx,ny,step;
}; 
node t;
queue<node> q;
inline int read(){
   int s=0,w=1;
   char ch=getchar();
   while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
   while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
   return s*w;
}
void bfs(){
	while(!q.empty()){
		t.nx=q.front().nx;
		t.ny=q.front().ny;
		t.step=q.front().step;
		if(mp[t.nx][t.ny]>t.step&&t.nx>1&&t.ny>1&&t.nx<=n&&t.ny<=m&&!p[t.nx][t.ny]){
			for(int i=0;i<8;i++){
				t.nx=q.front().nx+dx[i];
				t.ny=q.front().ny+dy[i];
				t.step=q.front().step+1;
				q.push(t);
			}
		}
		p[t.nx][t.ny]=1;
		q.pop();
	}
}
int main(){
	n=read(),m=read(),x=read(),y=read();
	n++,m++,x++,y++;
	memset(mp,0x7f7f7f7f,sizeof(mp));
	t.nx=x,t.ny=y,t.step=0;
	q.push(t);
	bfs();
	for(int i=2;i<=n;i++){
		for(int j=2;j<=m;j++){
			if(mp[i][j]==0x7f7f7f7f)printf("%-5d",-1);
			else printf("%-5d",mp[i][j]);
		}
		putchar('\n');
	}
}