Lowest Common Ancestor of a Binary Search Tree

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

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        _______6______       /              \    ___2__          ___8__   /      \        /      \   0      _4       7       9         /  \         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        int largerVal = p.val > q.val? p.val : q.val;        int smallerVal = p.val == largerVal? q.val:p.val;        return lowestCommonAncestorHelper(root, largerVal, smallerVal);    }        private TreeNode lowestCommonAncestorHelper(TreeNode root, int largerInput, int smallerInput){        if(smallerInput > root.val)            return lowestCommonAncestorHelper(root.right, largerInput, smallerInput);        else if(largerInput < root.val)            return lowestCommonAncestorHelper(root.left, largerInput, smallerInput);        else            return root;    }}