94. 二叉树的中序遍历

题目描述

给定一个二叉树，返回它的中序 遍历。

示例:

输入: [1,null,2,3]
   1
    \
     2
    /
   3

输出: [1,3,2]

进阶: 递归算法很简单，你可以通过迭代算法完成吗？

我的解法——递归（AC）

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def get_list(self, tree):
        if(not tree):
            return []
        left = self.get_list(tree.left)
        right = self.get_list(tree.right)
        return left + [tree.val, ] + right
    
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        return self.get_list(root)

我的解法——非递归（AC）

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        stack = []
        res = []
        now = root
        
        while(now):
            while(now):
                stack.append(now)
                now = now.left
            
            while(len(stack) and not stack[-1].right):
                res.append(stack[-1].val)
                del stack[-1]
                
            if(len(stack)):
                res.append(stack[-1].val)
                now = stack[-1].right
                del stack[-1]
            
        return res