HDU 5652 India and China Origins

二分答案+验证，注意一开始就不连通的话输出0

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn=500+50;
char s[maxn][maxn];
char tmp[maxn][maxn];
bool flag[maxn][maxn];
int dir[4][2]={
 {0,1},
 {0,-1},
 {1,0},
 {-1,0}
};

struct X
{
    int x,y;
}q[maxn*maxn];
int n,m,Q;

void read()
{
    scanf("%d%d",&n,&m);
    for(int i=0;i<n;i++) scanf("%s",s[i]);
    scanf("%d",&Q);
    for(int i=1;i<=Q;i++) scanf("%d%d",&q[i].x,&q[i].y);
}

bool P(int a,int b)
{
    if(a>=0&&a<n)
    {
        if(b>=0&&b<m)
        {
            if(tmp[a][b]=='0')
            {
                if(flag[a][b]==0)
                {
                    return 1;
                }
            }
        }
    }
    return 0;
}

void dfs(int x,int y)
{
    flag[x][y]=1;
    for(int i=0;i<4;i++)
    {
        int newx=x+dir[i][0];
        int newy=y+dir[i][1];
        if(P(newx,newy)) dfs(newx,newy);
    }
}

bool f(int year)
{
    for(int i=0;i<n;i++)
        for(int j=0;j<m;j++)
            tmp[i][j]=s[i][j];

    for(int i=1;i<=year;i++) tmp[q[i].x][q[i].y]='1';

    bool fail=1;
    for(int j=0;j<m;j++) if(tmp[0][j]=='0') fail=0;
    if(fail) return 1;

    fail=1;
    for(int j=0;j<m;j++) if(tmp[n-1][j]=='0') fail=0;
    if(fail) return 1;

    memset(flag,0,sizeof flag);
    for(int j=0;j<m;j++)
        if(tmp[0][j]=='0')
            dfs(0,j);

    fail=1;
    for(int j=0;j<m;j++)
        if(tmp[n-1][j]=='0'&&flag[n-1][j]==1) fail=0;
    return fail;
}

int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        read();
        if(f(0)) printf("0\n");
        else
        {
            int ans=-1;
            int left=1,right=Q;
            while(left<=right)
            {
                int mid=(left+right)/2;
                if(f(mid))
                {
                    ans=mid;
                    right=mid-1;
                }
                else
                {
                    left=mid+1;
                }
            }
            printf("%d\n",ans);
        }
    }
    return 0;
}