Last updated on October 5th, 2024 at 08:49 pm

Here, We see Lowest Common Ancestor of a Binary Search Tree LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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Lowest Common Ancestor of a Binary Search Tree LeetCode Solution

Problem Statement

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).”

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

1. Lowest Common Ancestor of a Binary Search Tree LeetCode Solution C++

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root==NULL) return nullptr;
        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;         
    }
};

2. Lowest Common Ancestor of a Binary Search Tree LeetCode Solution Java

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

3. Lowest Common Ancestor of a Binary Search Tree Solution JavaScript

var lowestCommonAncestor = function(root, p, q) {
    while (root) {
        if (root.val < p.val && root.val < q.val) {
            root = root.right;
        }
        else if (root.val > p.val && root.val > q.val) {
            root = root.left;
        } else {
            break;
        }
    }
    return root;    
};

4. Lowest Common Ancestor of a Binary Search Tree Solution Python

class Solution(object):
    def lowestCommonAncestor(self, root, p, q):
        if root:
            if root.val > p.val and root.val > q.val:
                return self.lowestCommonAncestor(root.left, p, q)
            elif root.val < p.val and root.val < q.val:
                return self.lowestCommonAncestor(root.right, p, q)
            else:
                return root