哪里错了？

#include<bits/stdc++.h>
using namespace std;
const int N=405;
struct point{
	int x,y,step;
};
int a[N][N];
int n,m,x,y;
int dx[8]={-2,-1,1,2,2,1,-1,-2},dy[8]={1,2,2,1,-1,-2,-2,-1};

void bfs(){
	queue<point> qu;
	a[x][y]=0;
	qu.push({x,y,0});
	while(!qu.empty()){
		point now=qu.front();
		qu.pop();
		for(int i=0;i<=8;i++){
			int _x,_y;
			_x=now.x+dx[i],_y=now.y+dy[i];
			if(_x>=1&&_x<=n&&_y>=1&&_y<=m&&a[_x][_y]==-1){
				a[_x][_y]=now.step+1;
				qu.push({_x,_y,a[_x][_y]});
			}
		} 
	}
}
int main(){
	cin>>n>>m>>x>>y;
	memset(a,-1,sizeof(a));
	bfs();
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++) cout<<setw(3)<<fixed<<left<<a[i][j];
	cout<<endl;
	}
	return 0;
}