---
tags: leetcode
---

# [235. Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/)
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# My Solution
## The Key Idea for Solving This Coding Question
## C++ Code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    TreeNode *lowestCommonAncestor(TreeNode *root, TreeNode *p, TreeNode *q) {
        while (root != nullptr) {
            if (p->val < root->val && q->val < root->val) {
                root = root->left;
            } else if (root->val < p->val && root->val < q->val) {
                root = root->right;
            } else {
                return root;
            }
        }

        return nullptr;
    }
};

## Time Complexity
$O(H)$
$H$ is the height of the BST referred by `root`.
## Space Complexity
$O(1)$
# Miscellane
<!--
# Test Cases
[6,2,8,0,4,7,9,null,null,3,5]
2
8

[6,2,8,0,4,7,9,null,null,3,5]
2
4

[2,1]
2
1

[6,2,8,0,4,7,9,null,null,3,5]
3
5

-->