add 101

Author: luliyucoordinate

README.md

@@ -101,6 +101,7 @@ LeetCode
 |0098|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/) | c | [c++](./src/0098-Validate-Binary-Search-Tree/0098.cpp) |[python](./src/0098-Validate-Binary-Search-Tree/0098.py)|||Medium|
 |0099|[Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/) | c | [c++](./src/0087-Scramble-String/0087.cpp) |[python](./src/0087-Scramble-String/0087.py)|||Hard|
 |0100|[Same Tree](https://leetcode.com/problems/same-tree/) | c | [c++](./src/0100-Same-Tree/0100.cpp) |[python](./src/0100-Same-Tree/0100.py)|||Easy|
+|0101|[Symmetric Tree](https://leetcode.com/problems/symmetric-tree/) | c | [c++](./src/0101-Symmetric-Tree/0101.cpp) |[python](./src/0101-Symmetric-Tree/0101.py)|||Easy|
 |0102|[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/) | c | [c++](./src/0102-Binary-Tree-Level-Order-Traversal/0102.cpp) |[python](./src/0102-Binary-Tree-Level-Order-Traversal/0102.py)|||Medium|
 |0103|[Binary Tree Zigzag Level Order Traversal](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) | c | [c++](./src/0103-Binary-Tree-Zigzag-Level-Order-Traversal/0103.cpp) |[python](./src/0103-Binary-Tree-Zigzag-Level-Order-Traversal/0103.py)|||Medium|
 |0104|[Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/) | c | [c++](./src/0104-Maximum-Depth-of-Binary-Tree/0104.cpp) |[python](./src/0104-Maximum-Depth-of-Binary-Tree/0104.py)|||Easy|

src/0101-Symmetric-Tree/0101.cpp

@@ -0,0 +1,18 @@
+static int x = []() {std::ios::sync_with_stdio(false); cin.tie(0); return 0; }();
+class Solution 
+{
+public:
+    bool isSymmetric(TreeNode* root) 
+    {
+        if (root == nullptr) return true;
+        return _isSymmetric(root->left, root->right);
+    }
+private:
+    bool _isSymmetric(TreeNode* left, TreeNode* right)
+    {
+        if (left == nullptr and right == nullptr) return true;
+        else if (left == nullptr or right == nullptr) return false;
+        else if (left->val != right->val) return false;
+        else return _isSymmetric(left->left, right->right) and _isSymmetric(left->right, right->left);
+    }
+};

src/0101-Symmetric-Tree/0101.py

@@ -0,0 +1,20 @@
+class Solution:
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if not root:
+            return True
+        
+        return self.helper(root.left, root.right)
+        
+    def helper(self, left, right):
+        if left == None and right == None:
+            return True
+        elif left == None or right == None:
+            return False
+        elif left.val != right.val:
+            return False
+        else:
+            return self.helper(left.left, right.right) and self.helper(left.right, right.left)