正题

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题目大意

一个迷宫，有许多出口，求一个点到最近的出口最远。

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解题思路

直接bfs暴力搜索，然后保存上次的答案

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code

// luogu-judger-enable-o2
#include<cstdio>
#include<queue>
#include<cstring>
#define N 210
using namespace std;
struct node{int x,y;
};
const int dx[4]={0,0,1,-1},dy[4]={1,-1,0,0};
int a[N][N],w,h,maxs;
char map[N][N];
queue<node> q;
void bfs(int xs,int ys)//搜索
{q.push((node){xs,ys});a[xs][ys]=0;while(!q.empty()){node x=q.front();q.pop();int ws=a[x.x][x.y];for(int i=0;i<4;i++) {int xx=dx[i]+x.x,yy=dy[i]+x.y;int zx=dx[i]*2+x.x,zy=dy[i]*2+x.y;if(zx<=h&&zx>0&&zy<=w&&zy>0&&map[xx][yy]==' '&&a[zx][zy]>ws+1){q.push((node){zx,zy});a[zx][zy]=ws+1;}}}
}
int main()
{memset(a,127/3,sizeof(a));scanf("%d%d",&w,&h);w=w*2+1;h=h*2+1;for(int i=0;i<=h;i++){gets(map[i]+1);for(int j=1;j<=w;j++)if(map[i][j]=='-'||map[i][j]=='+'||map[i][j]=='|')map[i][j]='+';else map[i][j]==' ';}for(int i=1;i<=h;i++){if(map[i][1]==' ')bfs(i,2);if(map[i][w]==' ')bfs(i,w-1);}for(int i=1;i<=w;i++){if(map[1][i]==' ')bfs(2,i);if(map[h][i]==' ')bfs(h-1,i);}for(int i=1;i<=h;i++)//{for(int j=1;j<=w;j++)//{if(a[i][j]<707406378)maxs=max(maxs,a[i][j]);//printf("%5d",a[i][j]);//else printf("%5d",100);//}printf("\n");}printf("%d",maxs+1);
}