LeetCode #257 Binary Tree Paths

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Problem

Given a binary tree, return all root-to-leaf paths.

Example

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Input:

   1
 /   \
2     3
 \
  5

Output: ["1->2->5", "1->3"]

Explanation: All root-to-leaf paths are: 1->2->5, 1->3

Solution

Method: Depth-first Search

Time Complexity: O(n)

Space Complexity: O(n)

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

class Solution:
    def binaryTreePaths(self, root):
        """
        :type root: TreeNode
        :rtype: List[str]
        """
        if not root:
            return []
        
        stack = [(root, [])]
        ret = []

        while stack:
            node, path = stack.pop()
            
            if node:
                val = str(node.val)
                if not node.left and not node.right:
                    complete_path = path + [val]
                    ret.append('->'.join(complete_path))
                else:
                    if node.left:
                        stack.append((node.left, path + [val]))
                    if node.right:
                        stack.append((node.right, path + [val]))
        
        return ret