hdu5652:India and China Origins（并查集）

#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#define ll long long 
using namespace std;
const int dx[5]={0,1,0,-1,0},dy[5]={0,0,1,0,-1},maxn=500010;
int n,m,china,india,T,q,fa[maxn],x[maxn],y[maxn];
bool v[510][510],map[510][510],map2[510][510];
char s[maxn];
void read(int &k)
{
    int f=1;k=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
    while(c<=‘9‘&&c>=‘0‘)k=k*10+c-‘0‘,c=getchar();
    k*=f;
}
int gf(int x){return fa[x]==x?x:fa[x]=gf(fa[x]);} 
int bh(int x,int y)
{
    if(x==0)return n*m+1;
    if(x==n+1)return n*m+2;
    return (x-1)*m+y;
}
void dfs(int x,int y)
{
    v[x][y]=1;
    for(int i=1;i<=4;i++)
    {
        int nx=x+dx[i],ny=y+dy[i];
        if(nx>n||nx<1||ny>m||ny<1)continue;
        if((!v[nx][ny])&&(!map[nx][ny])&&(!map2[nx][ny]))
        fa[gf(bh(nx,ny))]=gf(bh(x,y)),dfs(nx,ny);
    }
}
int main()
{
    read(T);
    while(T--)
    {
        memset(v,0,sizeof(v));
        memset(map,0,sizeof(map));
        memset(map2,0,sizeof(map2));
        read(n);read(m);china=n*m+1;india=n*m+2;
        for(int i=1;i<=n;i++)
        {
            scanf("%s",s);
            for(int j=0;j<m;j++)
            map[i][j+1]=s[j]-‘0‘;
        }
        read(q);
        for(int i=1;i<=q;i++)
        {
            read(x[i]);read(y[i]);
            x[i]++;y[i]++;
            map2[x[i]][y[i]]=1;
        }
        for(int i=1;i<=n*m+2;i++)fa[i]=i;
        for(int i=1;i<=m;i++)
        if((!map[1][i])&&(!v[1][i])&&(!map2[1][i]))fa[gf(bh(1,i))]=gf(china),dfs(1,i);
        for(int i=1;i<=m;i++)
        if((!map[n][i])&&(!v[n][i])&&(!map2[n][i]))fa[gf(bh(n,i))]=gf(india),dfs(n,i);
        for(int i=1;i<=n;i++)for(int j=1;j<=m;j++)
        if((!map[i][j])&&(!v[i][j])&&(!map2[i][j]))dfs(i,j);
        if(gf(china)==gf(india))printf("-1\n");
        else
        for(int i=q;i;i--)
        {
            map2[x[i]][y[i]]=0;
            for(int j=1;j<=4;j++)
            if((!map[x[i]+dx[j]][y[i]+dy[j]])&&(!map2[x[i]+dx[j]][y[i]+dy[j]]))
            fa[gf(bh(x[i]+dx[j],y[i]+dy[j]))]=gf(bh(x[i],y[i]));
            if(gf(china)==gf(india))
            {
                printf("%d\n",i);
                break;
            }
        }
    }
    return 0;
}