【Leetcode】235. Lowest Common Ancestor of a Binary Search Tree

算法描述
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).”

算法解析
二叉搜索树性质：
1）左子树（如果非空）上所有结点的关键码都小于根结点的关键码。
2）右子树（如果非空）上所有结点的关键码都大于根结点的关键码。

假设给定的两个结点的权值分别为 p和 q
1）如果root.val 比 p.val和 p.val都大，则它们的最低公共祖先结点在根的左子树中
2）如果root.val 比 node1 和 node2 都小,则它们的最低公共祖先结点在根的右子树中
3）如果root.val处于p.val 和 q.val之间，根就是它们的最低公共祖先结点

用递归来实现。

public class Solution {    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        if(root.val > p.val && root.val > q.val){            return lowestCommonAncestor(root.left, p, q);        }else if(root.val < p.val && root.val < q.val){            return lowestCommonAncestor(root.right, p, q);        }else{            return root;        }    }}