Leetcode 235. Lowest Common Ancestor of a Binary Search Tree

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

题目大意：已知一个BST，找到BST中的节点p+q的最小公共祖先；

思路：递归

1 boundary conditions: tree, p, q任意为null， 返回null

2 如果p.va, q.val均小于root.val -> 说明p，q都在左子树-> return LowestCommonAncestor(root.left, p, q);

3  如果p.va, q.val均大于root.val -> 说明p，q都在右子树-> return LowestCommonAncestor(root.right, p, q);

4 否则，说明一左一右->root即为最小公共祖先

/** * Definition for a binary tree node. * public class TreeNode { *     public int val; *     public TreeNode left; *     public TreeNode right; *     public TreeNode(int x) { val = x; } * } */

 public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {         if (p == null || q == null || root == null)            {                return null;            }            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;            }    }