Algorithm


Problem Name: 235. Lowest Common Ancestor of a Binary Search Tree

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

 

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.

Code Examples

#1 Code Example with C Programming

Code - C Programming


struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q) {
    if (root == NULL) {
        return NULL;
    }
    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;
}
Copy The Code & Try With Live Editor

Input

x
+
cmd
root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8

Output

x
+
cmd
6

#2 Code Example with C++ Programming

Code - C++ Programming

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        int Min = min(p->val, q->val);
        int Max = max(p->val, q->val);
        if(root->val  < = Max && root->val >= Min) return root;
        if(root->val > Max) return lowestCommonAncestor(root->left, p, q);
        return lowestCommonAncestor(root->right, p, q);
    }
};
Copy The Code & Try With Live Editor

Input

x
+
cmd
root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8

Output

x
+
cmd
6

#3 Code Example with Javascript Programming

Code - Javascript Programming


const lowestCommonAncestor = function(root, p, q) {
    while((root.val - p.val) * (root.val - q.val) > 0) {
          root = root.val > p.val ? root.left : root.right
    }
    return root
};
Copy The Code & Try With Live Editor

Input

x
+
cmd
root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4

Output

x
+
cmd
2

#4 Code Example with Python Programming

Code - Python Programming


class Solution:
    def lowestCommonAncestor(
        self, root: "TreeNode", p: "TreeNode", q: "TreeNode"
    ) -> "TreeNode":
        if p.val < root.val > q.val:
            return self.lowestCommonAncestor(root.left, p, q)
        if p.val > root.val < q.val:
            return self.lowestCommonAncestor(root.right, p, q)
        return root
Copy The Code & Try With Live Editor

Input

x
+
cmd
root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4

Output

x
+
cmd
2

#5 Code Example with C# Programming

Code - C# Programming


namespace LeetCode
{
    public class _0235_LowestCommonAncestorOfABinarySearchTree
    {
        public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
        {
            if (p.val > q.val) return LowestCommonAncestor(root, q, p);
            if (root.val >= p.val && root.val  < = q.val) return root;
            if (root.val < p.val && root.val < q.val) return LowestCommonAncestor(root.right, p, q);
            else return LowestCommonAncestor(root.left, p, q);
        }
    }
}
Copy The Code & Try With Live Editor

Input

x
+
cmd
root = [2,1], p = 2, q = 1

Output

x
+
cmd
2
Advertisements

Demonstration


Previous
#234 Leetcode Palindrome Linked List Solution in C, C++, Java, JavaScript, Python, C# Leetcode
Next
#236 Leetcode Lowest Common Ancestor of a Binary Tree Solution in C, C++, Java, JavaScript, Python, C# Leetcode