1644. Lowest Common Ancestor of a Binary Tree II

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree-ii

Description

Given the root of a binary tree, return the lowest common ancestor (LCA) of two given nodes, p and q. If either node p or q does not exist in the tree, return null. All values of the nodes in the tree are unique.

According to the definition of LCA on Wikipedia: "The lowest common ancestor of two nodes p and q in a binary tree T is the lowest node that has both p and q as descendants (where we allow a node to be a descendant of itself)". A descendant of a node x is a node y that is on the path from node x to some leaf node.

Example 1:

**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:

**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. A node can be a descendant of itself according to the definition of LCA.

Example 3:

**Input:** root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 10
**Output:** null
**Explanation:** Node 10 does not exist in the tree, so return null.

Constraints:

• The number of nodes in the tree is in the range [1, 104].

• -109 <= Node.val <= 109

• All Node.val are unique.

• p != q

Follow up: Can you find the LCA traversing the tree, without checking nodes existence?

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