235.LowestCommonAncestorofaBinarySearchTree.go

/*
235. Lowest Common Ancestor of a Binary Search Tree
Easy

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 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.
*/
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val   int
 *     Left  *TreeNode
 *     Right *TreeNode
 * }
 */

 func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
    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
    }
}