LeetCode

Problem Statement

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: 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, since a node can be a descendant of itself according to the LCA definition.

Solution

func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
	if root == nil {
		return nil
	}

	if root == p || root == q {
		return root
	}

	left := lowestCommonAncestor(root.Left, p, q)
	right := lowestCommonAncestor(root.Right, p, q)

	if left != nil && right != nil {
		return root
	}

	if left == nil {
		return right
	}

	if right == nil {
		return left
	}

	return nil
}