leetcode 94. 二叉树的中序遍历

'''
leetcode  94. 二叉树的中序遍历
给定一个二叉树，返回它的中序遍历
'''
# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def inorderTraversal(self, root: TreeNode):
        if root is None:
            return []
        if root.left is None and root.right is None:
            return [root.val]
        stack=[]# 构造辅助栈
        curr=root
        while(curr):
            stack.append(curr)
            curr=curr.left
        result=[]
        while(stack):
            curr=stack.pop(-1)
            # 当前节点出栈，说明当前节点的左子树中的所有元素都已经被访问完毕
            result.append(curr.val)
            if curr.right is not None:
                curr=curr.right
                while(curr):
                    stack.append(curr)
                    curr=curr.left
        return result

if __name__=="__main__":
    root=TreeNode(1)
    root.right=TreeNode(3)
    root.left=TreeNode(2)
    root.left.left=TreeNode(4)
    root.left.right=TreeNode(5)
    root.right.right=TreeNode(7)
    print(Solution().inorderTraversal(root))
    # [4,2,5,1,3,7]