[BZOJbegin][NOIP十连测热身赛b]escape（二分+bfs）

题目描述

题解

代码

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
using namespace std;
#define N 1005

int sx[4]={0,0,1,-1}; int sy[4]={1,-1,0,0};
int n,x,y,x1,y1,x2,y2,inf,ans,sum,cnt;
struct hp{int x,y;}pt[N*10];
int dis

,step

;
queue <hp> q;

bool check(int mid)
{
if (dis[x1][y1]<mid) return false;
while (!q.empty()) q.pop();
q.push((hp){x1,y1});
memset(step,127,sizeof(step));
step[x1][y1]=0;

while (!q.empty())
{
hp now=q.front(); q.pop();
for (int i=0;i<4;++i)
{
int u=now.x+sx[i],v=now.y+sy[i];
if (u<0||v<0||u>x||v>y||dis[u][v]<mid||step[u][v]!=inf) continue;
step[u][v]=step[now.x][now.y]+1;
if (u==x2&&v==y2)
{
cnt=step[u][v];
return true;
}
q.push((hp){u,v});
}
}
return false;
}
void find()
{
int l=0,r=2000,mid;
while (l<=r)
{
mid=(l+r)>>1;
if (check(mid)) ans=mid,sum=cnt,l=mid+1;
else r=mid-1;
}
}
int main()
{
scanf("%d%d%d",&n,&x,&y); x--; y--;
scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
memset(dis,127,sizeof(dis));inf=dis[0][0];
for (int i=1;i<=n;++i)
{
scanf("%d%d",&pt[i].x,&pt[i].y);
q.push((hp){pt[i].x,pt[i].y});
dis[pt[i].x][pt[i].y]=0;
}
while (!q.empty())
{
hp now=q.front(); q.pop();
for (int i=0;i<4;++i)
{
int u=now.x+sx[i],v=now.y+sy[i];
if (u<0||v<0||u>x||v>y||dis[u][v]!=inf) continue;
dis[u][v]=dis[now.x][now.y]+1;
q.push((hp){u,v});
}
}
find();
printf("%d %d\n",ans,sum);
}