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分享关于解Is it a tree的题
我现在在做一道关于树的题，看了半天没想出一个解决的方法来，网上搜到的解题方法没看明白，希望有人能帮我详细的解答一下，并讲解一下其中所用到的算法是如何实现的 谢谢了
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.
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.
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albzcj123 2012-07-18
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[Quote=引用 1 楼 的回复:]
楼主是不是缺少什么图片？为什么
For example, consider the illustrations below,
下面没有演示？？
[/Quote]
恩是 有图的这个是题目网址http://poj.org/problem?id=1308
楼主是不是缺少什么图片？为什么
For example, consider the illustrations below,
下面没有演示？？
[/Quote]
恩是 有图的这个是题目网址http://poj.org/problem?id=1308
cbzjzsb123 2012-07-16
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这边有AC的源码及解题报告
http://www.yidooo.net/archives/212.html
http://www.yidooo.net/archives/212.html
核动力蜗牛Killua 2012-07-16
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这边有AC的源码及解题报告
http://www.yidooo.net/archives/212.html
http://www.yidooo.net/archives/212.html
W170532934 2012-07-16
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楼主是不是缺少什么图片？为什么
For example, consider the illustrations below,
下面没有演示？？
For example, consider the illustrations below,
下面没有演示？？
