90pts WA on #10求条

#include <bits/stdc++.h>
using namespace std;
const int MAXN=505;
int dx[4]={0,-1,0,1};
int dy[4]={-1,0,1,0};
int step[MAXN][MAXN];
queue<pair<int,int> > q;
vector<pair<int,int> > lz;
int main() {
    ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	int n,m,a,b;
	cin>>n>>m>>a>>b;
	for (int i=1;i<=n;i++) {
		for (int j=1;j<=m;j++) {
			step[i][j]=0x3f;
		}
	}
	for (int i=1;i<=a;i++) {
		int x,y;
		cin>>x>>y;
		q.push(make_pair(x,y));
		step[x][y]=0;
	}
	for (int i=1;i<=b;i++) {
		int x,y;
		cin>>x>>y;
		lz.push_back(make_pair(x,y));
	}
	while (q.size()) {
		pair<int,int> u=q.front();
		q.pop();
		int x=u.first,y=u.second;
		for (int i=0;i<4;i++) {
			int xx=x+dx[i],yy=y+dy[i];
			if (step[xx][yy]>step[x][y]+1&&xx>=1&&xx<=n&&yy>=1&&yy<=m) {
				step[xx][yy]=step[x][y]+1;
				q.push(make_pair(xx,yy));
			}
		}
	}
	for (int i=0;i<lz.size();i++) {
		pair<int,int> u=lz[i];
		int x=u.first,y=u.second;
		cout<<step[x][y]<<'\n';
	}
	return 0;
}