以下代码实现的是一棵树的中序遍历：
TreeNode* root = new TreeNode{1};
root->left = new TreeNode{2};
root->right = new TreeNode{3};
root->left->left = new TreeNode{4};
g6-04967.in输出g6-04967.out以下代码实现的是一棵树的中序遍历：
TreeNode* root = new TreeNode{1};
root->left = new TreeNode{2};
root->right = new TreeNode{3};
root->left->left = new TreeNode{4};