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] = [x_i, y_i], and:

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 [x_i, y_i] exists in pairs if and only if x_i is an ancestor of y_i or y_i is an ancestor of x_i.
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:

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:

Class Solution

Constructor Summary