LeetCode 235. Lowest Common Ancestor of a Binary Search Tree

Question

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

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).”

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

Solution

• Solution1

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root.val > p.val && root.val > q.val) return lowestCommonAncestor(root.left, p, q);
        if (root.val < p.val && root.val < q.val) return lowestCommonAncestor(root.right, p, q);
        return root;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(h)