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1 | | -# [100. xxx](https://leetcode-cn.com/problems/recover-binary-search-tree) |
| 1 | +# [101. 对称二叉树](https://leetcode-cn.com/problems/symmetric-tree/description/) |
2 | 2 |
|
3 | 3 | ### 题目描述 |
4 | 4 |
|
| 5 | +<p>给定一个二叉树,检查它是否是镜像对称的。</p> |
| 6 | + |
| 7 | +<p> </p> |
| 8 | + |
| 9 | +<p>例如,二叉树 <code>[1,2,2,3,4,4,3]</code> 是对称的。</p> |
| 10 | + |
| 11 | +<pre> 1 |
| 12 | + / \ |
| 13 | + 2 2 |
| 14 | + / \ / \ |
| 15 | +3 4 4 3 |
| 16 | +</pre> |
| 17 | + |
| 18 | +<p> </p> |
| 19 | + |
| 20 | +<p>但是下面这个 <code>[1,2,2,null,3,null,3]</code> 则不是镜像对称的:</p> |
| 21 | + |
| 22 | +<pre> 1 |
| 23 | + / \ |
| 24 | + 2 2 |
| 25 | + \ \ |
| 26 | + 3 3 |
| 27 | +</pre> |
| 28 | + |
| 29 | +<p> </p> |
| 30 | + |
| 31 | +<p><strong>进阶:</strong></p> |
| 32 | + |
| 33 | +<p>你可以运用递归和迭代两种方法解决这个问题吗?</p> |
5 | 34 |
|
6 | 35 | ### 解题思路 |
7 | 36 |
|
| 37 | +1. 递归解法 |
8 | 38 |
|
9 | 39 | ### 具体解法 |
10 | 40 |
|
11 | | -<!-- tabs:start --> |
12 | 41 |
|
13 | 42 | #### **Golang** |
14 | 43 | ```go |
| 44 | +type TreeNode struct { |
| 45 | + Val int |
| 46 | + Left *TreeNode |
| 47 | + Right *TreeNode |
| 48 | +} |
15 | 49 |
|
| 50 | +func isSymmetric(root *TreeNode) bool { |
| 51 | + if root == nil { |
| 52 | + return true |
| 53 | + } |
| 54 | + return recursive(root.Left, root.Right) |
| 55 | +} |
| 56 | +func recursive(p, q *TreeNode) bool { |
| 57 | + if p == nil && q == nil { |
| 58 | + return true |
| 59 | + } |
| 60 | + if p == nil && q != nil { |
| 61 | + return false |
| 62 | + } |
| 63 | + if p != nil && q == nil { |
| 64 | + return false |
| 65 | + } |
| 66 | + return p.Val == q.Val && recursive(p.Left, q.Right) && recursive(p.Right, q.Left) |
| 67 | +} |
16 | 68 | ``` |
17 | 69 |
|
18 | | -<!-- tabs:end --> |
19 | 70 |
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