HDU-1272 小希的迷宫 并查集

#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;
}