Last updated on October 5th, 2024 at 06:07 pm

Here, We see Lowest Common Ancestor of a Binary 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 Tree LeetCode Solution

Problem Statement

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

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 = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
Output: 3
Explanation: The LCA of nodes 5 and 1 is 3.

Example 2:

Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
Output: 5
Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

Example 3:
Input: root = [1,2], p = 1, q = 2
Output: 1

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

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (!root || root == p || root == q) return root;
        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p, q);
        return !left ? right : !right ? left : root;        
    }
};

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

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null || root == p || root == q) return root;
        TreeNode left = lowestCommonAncestor(root.left, p, q);
        TreeNode right = lowestCommonAncestor(root.right, p, q);
        return left == null ? right : right == null ? left : root;        
    }
}

3. Lowest Common Ancestor of a Binary Tree Solution JavaScript

var lowestCommonAncestor = function(root, p, q) {
  if (!root || root === p || root === q) return root;
  var resL = lowestCommonAncestor(root.left, p, q);
  var resR = lowestCommonAncestor(root.right, p, q);
  return (resL && resR) ? root : (resL || resR);    
};

4. Lowest Common Ancestor of a Binary Tree Solution Python

class Solution(object):
    def lowestCommonAncestor(self, root, p, q):
        if root in (None, p, q): return root
        subs = [self.lowestCommonAncestor(kid, p, q)
                for kid in (root.left, root.right)]
        return root if all(subs) else max(subs)