257. Binary Tree Paths.py

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

# For example, given the following binary tree:

#    1
#  /   \
# 2     3
#  \
#   5
# All root-to-leaf paths are:

# ["1->2->5", "1->3"]
# Credits:
# Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.
# 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 binaryTreePaths(self, root):
        """
        :type root: TreeNode
        :rtype: List[str]
        """
        res = []
        if not root:
            return res
        self.helper(root, res, str(root.val))
        return res
    def helper(self, root, res, temp):
        if not root:
            return 
        if not root.left and not root.right:
            res.append(list(temp))
            return
        if root.left:
            self.helper(root.left, res, temp + '->'+str(root.left.val))
        if root.right:
            self.helper(root.right, res , temp + '->'+str(root.right.val))