From 2ba7e17b1cb01938b88912e823f2eb20d368756c Mon Sep 17 00:00:00 2001
From: Sainnhe Park <i@sainnhe.dev>
Date: Mon, 30 Jan 2023 20:35:13 +0800
Subject: [PATCH] s0101

---
 include/s0101_symmetric_tree.hpp | 11 +++++++++++
 src/s0101_symmetric_tree.cpp     | 17 +++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 include/s0101_symmetric_tree.hpp
 create mode 100644 src/s0101_symmetric_tree.cpp

diff --git a/include/s0101_symmetric_tree.hpp b/include/s0101_symmetric_tree.hpp
new file mode 100644
index 0000000..95be78f
--- /dev/null
+++ b/include/s0101_symmetric_tree.hpp
@@ -0,0 +1,11 @@
+#ifndef S0101_SYMMETRIC_TREE_HPP
+#define S0101_SYMMETRIC_TREE_HPP
+
+#include "structures.hpp"
+
+class S0101 {
+ public:
+  bool isSymmetric(TreeNode* root);
+};
+
+#endif
diff --git a/src/s0101_symmetric_tree.cpp b/src/s0101_symmetric_tree.cpp
new file mode 100644
index 0000000..58102b7
--- /dev/null
+++ b/src/s0101_symmetric_tree.cpp
@@ -0,0 +1,17 @@
+#include "s0101_symmetric_tree.hpp"
+
+bool isMirror(TreeNode *root1, TreeNode *root2) {
+  // 如果都为空指针则互为镜像
+  if (root1 == nullptr && root2 == nullptr) return true;
+  // 如果一个是空指针一个不是，则不互为镜像
+  if (root1 == nullptr || root2 == nullptr) return false;
+  // 如果根节点的值相等且...则互为镜像
+  return root1->val == root2->val && isMirror(root1->left, root2->right) &&
+         isMirror(root1->right, root2->left);
+}
+
+bool S0101::isSymmetric(TreeNode *root) {
+  // 对称树等价于根节点的左子树和右子树互为镜像
+  if (root == nullptr) return true;
+  return isMirror(root->left, root->right);
+}