Package g1701_1800.s1719_number_of_ways_to_reconstruct_a_tree

Class 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 Detail

      • Solution

        public Solution()

    • Method Detail

      • checkWays

        public int checkWays​(int[][] pairs)