hdu 5652 bestcoder 77 div2 2

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题意：

http://bestcoder.hdu.edu.cn/contests/contest_chineseproblem.php?cid=682&pid=1003

思路：

二分最先 A 不能到达B 的值，判断A 是否能到达B 广搜标记就可了

#include<bits/stdc++.h>using namespace std;const int maxn = 505;char a[maxn][maxn];char b[maxn][maxn];int vis[maxn][maxn];int dri[4][2] = {{0,1},{0,-1},{-1,0},{1,0} };struct node{    int x,y ;} c[maxn*maxn];int n,m;bool bfs(){  memset(vis,0,sizeof(vis));    queue<node>q;    node s;    for(int j= 0; j<m; j++)    {        if(b[0][j]=='0')        {            s.x= 0;            s.y =j;            q.push(s);        }    }    while(!q.empty())    {        node now = q.front();        q.pop();        if(now.x==n-1)            return true;        for(int i = 0; i<4; i++)        {            node next ;            next.x = now.x+dri[i][0];            next.y = now.y +dri[i][1];            if(vis[next.x][next.y]==0&&next.x>=0&&next.y>=0&&next.x<n&&next.y<m&&b[next.x][next.y]=='0')            {                q.push(next);                vis[next.x][next.y] =1;            }        }    }    return false ;}bool slove(int x){  memset(b,0,sizeof(b));    for(int i = 0; i<n; i++)        for(int j =0; j<m; j++)        {            b[i][j]  = a[i][j];        }    for(int  i = 1; i<=x; i++)    {        b[c[i].x][c[i].y] = '1';    }    if(bfs())return true;    return false;}int main(){    int T;    scanf("%d",&T);    while(T--)    {        scanf("%d%d",&n,&m);        for(int i = 0; i<n; i++)            scanf("%s",a[i]);            int q;            cin>>q;        for(int i = 1; i<=q; i++)            scanf("%d%d",&c[i].x,&c[i].y);        int l  = 1;        int  r = q;        while(l<=r)        {            int mid = (l+r)>>1;            if(slove(mid))            {                 l = mid+1;            }            else r = mid-1;        }        if(l==q){puts("-1");continue;}        printf("%d\n",l);    }    return 0;}

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