Nyoj129 decision tree [and query set]

Decision time limit of tree: 1000 MS | memory limit: 65535 kb difficulty: 4

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 should t 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 specified strations 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.

The number of test cases will not more than 20, and the number of the node will not exceed 10000.
The inputs will be ended by a pair of-1.

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 08 1  7 3  6 2  8 9  7 5 7 4  7 8  7 6  0 03 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

Poj

Uploaded

Zhang yuncong

Determine whether a directed graph is a tree. Question: If a graph is a tree, the following conditions must be met: 1. The number of trees cannot be greater than 1, and the empty tree is also a tree; 2. the node input level cannot be greater than 1; 3. It cannot be a ring. For example, it is illegal for a leaf node of a tree to point to the root node. 4. The self-ring is invalid.

#include <stdio.h>#include <string.h>#define maxn 10010int pre[maxn];bool vis[maxn];int unionFind(int k){int a = k, b;while(pre[k] != -1) k = pre[k];while(a != k){b = pre[a];pre[a] = k;a = b;}return k;}int main() {// freopen("stdin.txt", "r", stdin);memset(pre, -1, sizeof(pre));int u, v, cas = 1, ok = 1, count = 0;while(scanf("%d%d", &u, &v) != EOF) {if(u < 0) break;if(!(u | v)) {printf("Case %d ", cas++);if(count > 1) ok = 0;if(ok) printf("is a tree.\n");else printf("is not a tree.\n");memset(pre, -1, sizeof(pre));memset(vis, 0, sizeof(vis));count = 0; ok = 1; continue;}if(!ok) continue;if(!vis[u]) {vis[u] = 1; ++count;}if(!vis[v]) {vis[v] = 1; ++count;}if(pre[v] != -1 || u == v) {ok = 0; continue;}u = unionFind(u);if(u == v) {ok = 0; continue;}pre[v] = u; --count;}return 0;}

Nyoj129 decision tree [and query set]