Package 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:** ![](https://assets.leetcode.com/uploads/2020/12/03/trees2.png) **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:** ![](https://assets.leetcode.com/uploads/2020/12/03/tree.png) **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 Details

    • Solution

      public Solution()

  • Method Details

    • checkWays

      public int checkWays(int[][] pairs)