hdu 1257 小希的迷宫 并查集

题目链接:

题意:

题解:

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define MS(a) memset(a,0,sizeof(a))
#define MP make_pair
#define PB push_back
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline ll read(){
ll x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
return x*f;
}
//////////////////////////////////////////////////////////////////////////
const int maxn = 1e5+10;

int mark[maxn],fa[maxn];

int find(int x){
return fa[x]==x ? x : fa[x]=find(fa[x]);
}

bool Union(int u,int v){
int t1 = find(u), t2 = find(v);
if(t1 == t2) return false;
fa[t1] = t2;
return true;
}

int main(){
int a,b;
while(scanf("%d%d",&a,&b)){
if(a==-1 && b==-1) break;
if(a==0 && b==0){
puts("Yes");
continue;
}

MS(mark);
for(int i=0; i<=maxn; i++)
fa[i] = i;

mark[a] = mark[b] = 1;
fa[a] = b;
int flag = 1;
while(scanf("%d%d",&a,&b) && (a+b)){
mark[a] = mark[b] = 1;
if(Union(a,b)==0)
flag = 0;
}
if(flag==0)
puts("No");
else{
int cnt = 0;
for(int i=1; i<=maxn; i++){
if(mark[i] && fa[i]==i)
cnt++;
}
if(cnt == 1)
puts("Yes");
else
puts("No");
}
}

return 0;
}