题解 | 二叉树的中序遍历-栈的使用

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return int整型一维数组
#
class Solution:
    # 递归写法
    def inorderTraversal_1(self , root: TreeNode) -> List[int]:
        # write code here
        """
        1.  左----中----右 

        """
        ans =[]
        def  dfs(root):
            if root is None:
                return 
            if root.left:
                dfs(root.left)
            
            ans.append(root.val)
            if root.right:
                dfs(root.right)
        dfs(root)
        return ans 
    # 非递归
    def inorderTraversal(self , root: TreeNode) -> List[int]:
        stack =[]
        res=[]
        cur =root
        while stack or  cur :
            
            while cur: # 一直遍历左子树
                stack.append(cur)
                print(cur.val)
                cur=cur.left
            node =stack.pop()
            
            res.append(node.val) 

            if node.right:
                cur=node.right
                
        return res