• hdu 1325 is it a tree?


    网上一搜全是并查集。。 并查集POJ可以水过,HDU就不行了。。

    并查集的话:

     1 #include<iostream>
     2 #include<cstdio>
     3 #include<cstring>
     4 using namespace std;
     5 int pre[1005];
     6 bool vis[1005];
     7 int num[1005];
     8 bool flag;
     9 int x,y,icase=1;
    10 void init()
    11 {
    12     for(int i=0;i<=1000;i++)
    13         pre[i]=i;
    14     memset(num,0,sizeof(num));
    15     memset(vis,false,sizeof(vis));
    16     flag=false;
    17 }
    18 int find(int x)
    19 {
    20     if(pre[x]!=x)
    21         pre[x]=find(pre[x]);
    22     return pre[x];
    23 }
    24 void judge()
    25 {
    26     for(int i=1;i<=1000;i++)
    27         if(vis[i]) num[find(i)]++;
    28     int key=0;
    29     for(int i=1;i<=1000;i++)
    30         if(num[i]>1) key++;
    31     if(key>1) flag=true;
    32 }
    33 int main()
    34 {
    35 //    freopen("in.txt","r",stdin);
    36     init();
    37     while(1)
    38     {
    39         scanf("%d%d",&x,&y);
    40         if(x<0 && y<0)
    41             break;
    42         else if(x==0 && y==0)
    43         {
    44             judge();
    45             if(flag)
    46                 printf("Case %d is not a tree.
    ",icase++);
    47             else
    48                 printf("Case %d is a tree.
    ",icase++);
    49             init();
    50             continue;
    51         }
    52         else
    53         {
    54             vis[x]=vis[y]=true;
    55             if(find(x)==find(y) || pre[y]!=y)
    56                 flag=true;
    57             else
    58                 pre[y]=x;
    59         }
    60     }
    61     return 0;
    62 }
    迪哥代码

    有个坑是只要是输入两个负数就结束,不一定是-1 -1

    判断图是否为树:1.是否为连通图  2.是否有环

    因为题目给的是从父亲指向儿子,所以直接判断点的入度就可以了

     1 #include "iostream"
     2 #include "memory.h"
     3 #include "cstdio"
     4 using namespace std;
     5 #define MAXN 1111
     6 int fa[MAXN];
     7 int in_degree[MAXN];
     8 bool c[MAXN];
     9 bool ok;
    10 
    11 int main()
    12 {
    13     int a,b,T = 1;
    14     while (~scanf("%d%d",&a,&b)) {
    15         memset(fa,-1,sizeof(fa));
    16         memset(in_degree,0,sizeof(in_degree));
    17         memset(c,0,sizeof(c));
    18         if (a < 0 && b < 0) break;
    19         c[a] = 1;
    20         c[b] = 1;
    21         in_degree[b]++;
    22         while (~scanf("%d%d",&a,&b),a+b) {
    23             if (a < 0 && b < 0) return 0;
    24             in_degree[b]++;
    25             c[a] = 1;
    26             c[b] = 1;
    27         }
    28         int re = 0;
    29         int ok = 1;
    30         for (int i = 0;i < MAXN; ++ i) if (c[i]){
    31             if (in_degree[i] == 0) re ++;
    32             if (in_degree[i] > 1) ok = 0;
    33         }
    34         if (re == 1 && ok) printf("Case %d is a tree.
    ",T);
    35         else printf("Case %d is not a tree.
    ",T);
    36         T++;
    37     }
    38     return 0;
    39 }
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  • 原文地址:https://www.cnblogs.com/usedrosee/p/4241805.html
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