235 Lowest Common Ancestor of a Binary Search Tree

So, the lowest common ancestor for any two nodes (p and q) in a BST is termed as the minimum value node that contains both p and q in their sub trees. The lowest common ancestor for any node is itself or some previous node.

Code:

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.right, p, q);
        }
        if (p.val < root.val && q.val < root.val) {
            return lowestCommonAncestor(root.left,p,q);
        }
        return root;
    }
}

Big O Analysis

• Runtime The runtime complexity here is O(N) .
• Memory The memory usage is O(N) since we would use the implicit call stack.

— A

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