zoukankan      html  css  js  c++  java
  • TOJ 1856 Is It A Tree?

    Description

    A tree is a well-known data structure that is either empty (null, void, nothing) or is a set of one or more nodes connected by directed edges between nodes satisfying the following properties.

    There is exactly one node, called the root, to which no directed edges point.

    Every node except the root has exactly one edge pointing to it.

    There is a unique sequence of directed edges from the root to each node.

    For example, consider the illustrations below, in which nodes are represented by circles and edges are represented by lines with arrowheads. The first two of these are trees, but the last is not.

    In this problem you will be given several descriptions of Collections of nodes connected by directed edges. For each of these you are to determine if the collection satisfies the definition of a tree or not.

    Input

    The input will consist of a sequence of descriptions (test cases) followed by a pair of negative integers. Each test case will consist of a sequence of edge descriptions followed by a pair of zeroes Each edge description will consist of a pair of integers; the first integer identifies the node from which the edge begins, and the second integer identifies the node to which the edge is directed. Node numbers will always be greater than zero.

    Output

    For each test case display the line ``Case k is a tree." or the line ``Case k is not a tree.", where k corresponds to the test case number (they are sequentially numbered starting with 1).

    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

    Case 1 is a tree.
    Case 2 is a tree.
    Case 3 is not a tree.

    Source

    North Central North America 1997

    只要判断必须有一个结点的入度为0,所有结点的入度不能大于1。

    如果没有结点也是成立的。(坑)

     1 #include <stdio.h>
     2 #include <string.h>
     3 #include <set>
     4 #define MAXN 100010
     5 using namespace std;
     6 
     7 int indegree[MAXN];
     8 set<int> S;
     9 set<int>::iterator it;
    10 
    11 bool judege(){
    12     int flag=0;
    13     for(it=S.begin(); it!=S.end(); it++){
    14         if(indegree[*it]==0)flag++;
    15         if(indegree[*it]>1)return false;
    16     }
    17     if(flag==1)return true;
    18     else return false;
    19 }
    20 
    21 int main()
    22 {
    23     int c=0;
    24     int u,v;
    25     while( scanf("%d %d" ,&u ,&v)!=EOF ){
    26         if(u==-1 && v==-1)break;        
    27         if(u==0 && v==0){
    28             if(judege() || S.size()==0){
    29                 printf("Case %d is a tree.
    ",++c);
    30             }else{
    31                 printf("Case %d is not a tree.
    ",++c);
    32             }
    33             memset(indegree ,0 ,sizeof(indegree));
    34             S.clear();
    35         }else{
    36             indegree[v]++; 
    37             S.insert(u);
    38             S.insert(v);
    39         }
    40     }
    41     return 0;
    42 }
  • 相关阅读:
    PostThreadMessage
    WaitForSingleObject函数的使用
    CodeWarrior环境下中断使用
    Activity跳转时生命周期跟踪
    win7 VS2012+openCV-2.4.11 配置
    CodeBlocks16.01+wxWidgets3.0.2
    MFC一个类访问另一个类成员对象的成员变量值
    无法打开包括文件:'atlrx.h'的解决办法
    STM32f103的数电采集电路的TIMER定时器的使用与时序控制的程序
    STM32f103的数电采集电路的双ADC的设计与使用
  • 原文地址:https://www.cnblogs.com/chenjianxiang/p/3579999.html
Copyright © 2011-2022 走看看