LeetCode Lowest Common Ancestor of a Binary Tree

原题链接在这里：https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/

是Lowest Common Ancestor of a Binary Search Tree的进阶题目。无法比较大小，但是可以看p,q是不是在root的两边，若在两边，则返回root.
若都在一边，就在那一边继续。

Note: 1. 若有root == p || root == q时，需比较原来的点而不单单是val, 这里可以有重复的值，在能比较整体点时就不比较val.

2. 递归终止条件这里有两个，一个是root == null, 一个是root等于p或者q, 这两个终止条件缺一不可。

AC Java:

/**
* 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(root == null){
return root;
}
if(root == p || root == q){
return root;
}
TreeNode left = lowestCommonAncestor(root.left,p,q);
TreeNode right = lowestCommonAncestor(root.right,p,q);
if(left != null && right != null){
return root;
}else if(left != null){
return left;
}else if(right != null){
return right;
}else{
return null;
}
}
}