Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

    1    
/ \
2 5
/ \ \
3 4 6

The flattened tree should look like:

1  
\
2
\
3
\
4
\
5
\
6
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def flatten(self, root: TreeNode) -> None:
        """
        Do not return anything, modify root in-place instead.
        """
        node, stack = root, []
        
        while node:
            if node.right:
                stack.append(node.right)
            node.right = node.left
            node.left = None
            
            if not node.right and stack:
                temp = stack.pop()
                node.right = temp
            
            node = node.right

Leave a Reply

Your email address will not be published. Required fields are marked *