LeetCode - 235. Lowest Common Ancestor of a Binary Search Tree(Tree, DFS, Binary Tree)*

문제

Given a binary search tree (BST), find the lowest common ancestor (LCA) node 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/description/

Example 1:

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.

Example 2:

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.

Example 3:

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

풀이

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

        
    }
}