Leetcode-lowest Common Ancestor of a Binary Search Tree

Given A binary search tree (BST), find the lowest common ancestor (LCA) of the Given nodes in the BST. According to the definition of the LCA in Wikipedia: "The lowest common ancestor is defined between," nodes V and W as the L Owest node in T, have 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   52 and 8 is 6. Another example is LCA of nodes 2 and 4 are 2, since a node can be a descendant of itself according to the LCA definition.

Idea, first determine whether the entry has illegal input.

1 if a certain root==p | | root = q, then the LCA must be root (because the top Down,lca is definitely in the root tree, and root is P q one node, then the other node must be under root, then root is the LCA), then return to root

2 if Root<min (p, Q), then the LCA must be on the right subtree, then recursion

3 if Max (P, q) <root, then the LCA must be on the left subtree, then recursion

4 if p<root<q, then root must be LCA

/** * 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) {/*        if (p = = Root | | q = = Root | | root = null) {return root;        } TreeNode Left=lowestcommonancestor (Root.left, p, q);        TreeNode right=lowestcommonancestor (Root.right, p, q);        On both sides if (left! = null && right! = null) return root;            On one side if (left! = null) {} */if (Root==null | | root = = P | | root = = q) {        return root;        } if (Root.val < Math.min (P.val, Q.val)) {return lowestcommonancestor (Root.right, p, q);        } else if (Root.val > Math.max (p.val, Q.val)) {return lowestcommonancestor (Root.left, p, q);        } else {return root;    }}} 

　　

Leetcode-lowest Common Ancestor of a Binary Search Tree