StarWalker

Where my heart will take me

0%

Leetcode236-lowestCommonAncestorOfABinaryTree

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

Given the following binary tree: root = [3,5,1,6,2,0,8,null,null,7,4]

;

Example

Example 1:

1
2
3
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
Output: 3
Explanation: The LCA of nodes 5 and 1 is 3.

Example 2:
1
2
3
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
Output: 5
Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

Solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null || root.val == p.val || root.val == q.val) return root;
        TreeNode leftTree = lowestCommonAncestor(root.left, p, q);
        TreeNode rightTree = lowestCommonAncestor(root.right, p, q);
        if (leftTree != null && rightTree != null) return root;
        return leftTree == null ? rightTree : leftTree;
    }
}