为何我样例过了全WA呢，悬关

#include <bits/stdc++.h>
using namespace std;
int b[3000][3000],n,aa[3000][3000],m,sum,k,p,x,y,ax[4]={1,0,-1,0},ay[4]={0,1,0,-1}; 
char a[3000][3000];
struct kkk{
    int x,y,k;
};
queue<kkk> s;
int main() {
    cin>>n>>m>>k>>p;
    for(int i=1;i<=k;i++){
    	cin>>x>>y;
    	s.push((kkk){x,y,0});
    }
    while(!s.empty()){
    	kkk f=s.front();
		for(int i=0;i<=3;i++){
            int bx=f.x+ax[i];
            int by=f.y+ay[i];
            if(bx>=1&&bx<=n&&by>=1&&by<=m&&b[bx][by]==0){
            	//cout<<bx<<" "<<by<<" "<<f.k<<endl;
                s.push((kkk){bx,by,f.k+1});
                b[bx][by]=1;
                aa[bx][by]=f.k+1;
            }
        }
        s.pop();
	}
	for(int i=1;i<=p;i++){
    	cin>>x>>y;
    	cout<<aa[x][y]<<endl;
    }
    return 0;
}