今天做题发现了一道对递归最佳辅助理解的题目：剑指 Offer 68 - II. 二叉树的最近公共祖先，二叉树对理解递归的帮助很大。
1 /**
2 * Definition for a binary tree node.
3 * public class TreeNode {
4 * int val;
5 * TreeNode left;
6 * TreeNode right;
7 * TreeNode(int x) { val = x; }
8 * }
9 */
10 class Solution {
11 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
12 if (root == null || root == p || root == q) {
13 return root;
14 }
15 TreeNode left = lowestCommonAncestor(root.left, p, q);
16 TreeNode right = lowestCommonAncestor(root.right, p, q);
17 if (left == null && right == null) {
18 return null;
19 }
20 if (left == null) {
21 return right;
22 }
23 if (right == null) {
24 return left;
25 }
26 return root;
27 }
28 }