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website/content/ChapterFour/0101.Symmetric-Tree.md

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+# [101. Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)
+
+## 题目
+
+
+Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
+
+For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
+
+
+```
+
+    1
+   / \
+  2   2
+ / \ / \
+3  4 4  3
+
+```
+
+But the following [1,2,2,null,3,null,3] is not:
+
+```
+
+    1
+   / \
+  2   2
+   \   \
+   3    3
+
+```
+
+**Note**:   
+
+Bonus points if you could solve it both recursively and iteratively.
+
+## 题目大意
+
+这一题要求判断 2 颗树是否是左右对称的。
+
+
+## 解题思路
+
+- 这道题是几道题的综合题。将根节点的左字数反转二叉树，然后再和根节点的右节点进行比较，是否完全相等。
+- 反转二叉树是第 226 题。判断 2 颗树是否完全相等是第 100 题。
+
+
+
+
+## 代码
+
+```go
+
+package leetcode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func isSymmetric(root *TreeNode) bool {
+	if root == nil {
+		return true
+	}
+	return isSameTree(invertTree(root.Left), root.Right)
+}
+
+```