• hdu 1272 判断所给的图是不是生成树 (并查集)


    判断所给的图是不是生成树,如果有环就不是,如果没环但连通分量大于1也不是

    find函数 用递归写的话 会无限栈溢出 Orz
    要加上那一串 手动扩栈

    Sample Input
    6 8 5 3 5 2 6 4
    5 6 0 0

    8 1 7 3 6 2 8 9 7 5
    7 4 7 8 7 6 0 0

    3 8 6 8 6 4
    5 3 5 6 5 2 0 0

    -1 -1

    Sample Output
    Yes
    Yes
    No

     1 # include <iostream>
     2 # include <cstdio>
     3 # include <cstring>
     4 # include <algorithm>
     5 # include <cmath>
     6 # include <queue>
     7 # define LL long long
     8 #pragma comment(linker, "/STACK:1024000000,1024000000")
     9 using namespace std ;
    10 
    11 const int MAXN=100010;
    12 int F[MAXN];
    13 bool vis[MAXN] ;
    14 int save[MAXN] ;
    15 bool flag ;
    16 int find(int x)//找x的祖先结点
    17 {
    18     if(F[x]==x) return x;
    19     return F[x]=find(F[x]);
    20 }
    21 void bing(int u,int v)
    22 {
    23     int t1=find(u);
    24     int t2=find(v);
    25     if(t1!=t2) F[t1]=t2;
    26     else flag = 1 ; //有环
    27 }
    28 int main()
    29 {
    30     //freopen("in.txt","r",stdin) ;
    31     int u , v ;
    32     while(scanf("%d %d" , &u , &v) != EOF)
    33     {
    34         if (u == -1 && v == -1)
    35             break ;
    36         if (u == 0 && v == 0)
    37         {
    38             printf("Yes
    ") ;
    39             continue ;
    40         }
    41          int i ;
    42          for(i=1;i<MAXN;i++)
    43          {
    44              F[i]=i;
    45          }
    46         memset(vis , 0 , sizeof(vis)) ;
    47         F[u] = v ;
    48         int l = 0 ;
    49         flag = 0 ;
    50         if (!vis[u])
    51         {
    52             vis[u] = 1 ;
    53             save[l++] = u ;
    54         }
    55         if (!vis[v])
    56         {
    57             vis[v] = 1 ;
    58             save[l++] = v ;
    59         }
    60         while(scanf("%d %d" , &u , &v))
    61         {
    62             if (u == 0 && v == 0)
    63                break ;
    64             if (flag)
    65                 continue ;
    66             if (!vis[u])
    67         {
    68             vis[u] = 1 ;
    69             save[l++] = u ;
    70         }
    71             if (!vis[v])
    72         {
    73             vis[v] = 1 ;
    74             save[l++] = v ;
    75         }
    76             bing(u,v) ;
    77         }
    78         int res = 0 ; //连通分量
    79         for (i = 0 ; i < l ; i++)
    80             if (F[save[i]] == save[i])
    81                 res++ ;
    82         if (res >= 2 || flag == 1)
    83             printf("No
    ") ;
    84         else
    85             printf("Yes
    ") ;
    86     }
    87     return 0;
    88 }
    View Code
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  • 原文地址:https://www.cnblogs.com/mengchunchen/p/4595170.html
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