今天浅浅复习巩固一下bfs

答案：

#include<iostream>
#include<algorithm>
#include<cstring>using namespace std;
typedef pair<int,int> PII;const int N=510; 
int n,m,a,b;
int dist[N][N];
PII q[N*N];
int hh=0,tt=-1;int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};void bfs(){while(hh<=tt){PII t=q[hh++];for(int i=0;i<4;i++){int a=t.first+dx[i];int b=t.second+dy[i];if(a<1||a>n||b<1||b>m) continue;if(dist[a][b]>=0) continue;dist[a][b]=dist[t.first][t.second]+1;q[++tt]={a,b};}}}int main()
{scanf("%d %d %d %d",&n,&m,&a,&b);memset(dist,-1,sizeof dist);while(a--){int x,y;scanf("%d %d",&x,&y);//q[tt++]={x,y};q[++tt]={x,y};dist[x][y]=0;	}bfs();while(b--){int x,y;scanf("%d %d",&x,&y);printf("%d\n",dist[x][y]);}return 0;}