在洛谷上被卡了一个点开了O2才过= =

bfs即可，为方便存储，把所有坐标+500

#include<iostream>

#include<cstdio>

#include<queue>

using namespace std;

const int N=1005,dx[]={-1,1,0,0},dy[]={0,0,-1,1};

int n,sx,sy;

bool a[N][N],v[N][N];

struct qwe

{

	int x,y,b;

	qwe(int X=0,int Y=0,int B=0)

	{

		x=X,y=Y,b=B;

	}

};

int read()

{

	int r=0,f=1;

	char p=getchar();

	while(p>'9'||p<'0')

	{

		if(p=='-')

			f=-1;

		p=getchar();

	}

	while(p>='0'&&p<='9')

	{

		r=r*10+p-48;

		p=getchar();

	}

	return r*f;

}

bool ok(int x,int y)

{

	return x>=0&&y>=0&&x<=1000&&y<=1000&&!v[x][y]&&!a[x][y];

}

int main()

{

	sx=read()+500,sy=read()+500,n=read();

	for(int i=1;i<=n;i++)

	{

		int x=read()+500,y=read()+500;

		a[x][y]=1;

	}

	queue<qwe>q;

	q.push(qwe(500,500,0));

	v[500][500]=1;

	while(!q.empty())

	{

		int x=q.front().x,y=q.front().y,b=q.front().b;

		if(x==sx&&y==sy)

		{

			printf("%d\n",b);

			break;

		}

		q.pop();

		v[x][y]=0;

		for(int i=0;i<4;i++)

			if(ok(x+dx[i],y+dy[i]))

				q.push(qwe(x+dx[i],y+dy[i],b+1)),v[x+dx[i]][y+dy[i]]=1;

	}

	return 0;

}