g1701_1800.s1719_number_of_ways_to_reconstruct_a_tree

Class Solution

java.lang.Object

g1701_1800.s1719_number_of_ways_to_reconstruct_a_tree.Solution

public class Solution
extends Object

1719 - Number Of Ways To Reconstruct A Tree.

Hard

You are given an array pairs, where pairs[i] = [xi, yi], and:

• There are no duplicates.
• xi < yi

Let ways be the number of rooted trees that satisfy the following conditions:

• The tree consists of nodes whose values appeared in pairs.
• A pair [xi, yi] exists in pairs if and only if xi is an ancestor of yi or yi is an ancestor of xi.
• Note: the tree does not have to be a binary tree.

Two ways are considered to be different if there is at least one node that has different parents in both ways.

Return:

• 0 if ways == 0
• 1 if ways == 1
• 2 if ways > 1

A rooted tree is a tree that has a single root node, and all edges are oriented to be outgoing from the root.

An ancestor of a node is any node on the path from the root to that node (excluding the node itself). The root has no ancestors.

Example 1:

Input: pairs = [[1,2],[2,3]]

Output: 1

Explanation: There is exactly one valid rooted tree, which is shown in the above figure.

Example 2:

Input: pairs = [[1,2],[2,3],[1,3]]

Output: 2

Explanation: There are multiple valid rooted trees. Three of them are shown in the above figures.

Example 3:

Input: pairs = [[1,2],[2,3],[2,4],[1,5]]

Output: 0

Explanation: There are no valid rooted trees.

Constraints:

• 1 <= pairs.length <= 105
• 1 <= xi < yi <= 500
• The elements in pairs are unique.

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	checkWays(int[][] pairs)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

checkWays

public int checkWays(int[][] pairs)