0235 - Lowest Common Ancestor of a Binary Search Tree

0235 - Lowest Common Ancestor of a Binary Search Tree

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).”

Examples

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6.

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

Input: root = [2,1], p = 2, q = 1 Output: 2

Constraints

The number of nodes in the tree is in the range [2, 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.

Java Solution

/**
 * 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(p.val > root.val && q.val > root.val) return lowestCommonAncestor(root.right, p, q);
        else if (p.val < root.val && q.val < root.val) return lowestCommonAncestor(root.left, p, q);
        else return root;     
    }
}