HDU-1272 小希的迷宮 並查集

題目連結

#include "stdio.h"
const int maxn = 100050;
int p[maxn],rank[maxn];
bool vis[maxn];
int n,flag;
int find( int x )
{
    return p[x] == x ? x:p[x] = find(p[x]);
}
void merge( int a,int b )
{
    int x = find(a);
    int y = find(b);
    if( x!=y )
        if( rank[x] > rank[y] )
			p[y] = x;
		else
		{
			p[x] = y;
			if( rank[x] == rank[y] )
				rank[y]++;
		}
    else
        flag = 0;
}
int main()
{
    int a,b;
    while( scanf("%d%d",&a,&b)==2 ,( a!=-1 || b!=-1 ) )
    {
        if( !a || !b )
        {
            puts("Yes");
            continue;
        }
        for( int i = 0; i < maxn; i ++ )
        {
            p[i]= i;
            vis[i]=0;
			rank[i] = 0;
        }
        vis[a] = vis[b] = 1;
        flag = 1;
        merge(a,b);
        while( scanf("%d%d",&a,&b)==2,(a||b) )
        {
            merge(a,b);
            vis[a] = vis[b] = 1;
        }
        int k = 0;
        for( int i = 1; i < maxn; i ++ )
        {
            if( vis[i] && p[i]==i )
            {
                k++;
            }
            if( k>1 )
                flag = 0;
        }
        if( flag )
            puts("Yes");
        else
            puts("No");
    }
    return 0;
}