递归实现

https://leetcode-cn.com/problems/binary-tree-inorder-traversal/submissions/

非递归实现

https://leetcode-cn.com/problems/binary-tree-inorder-traversal/submissions/

  1. 非递归实现的关键在于理清楚在递归实现过程中的入栈、出栈情况; 中序遍历非递归实现