Sum Root to Leaf Numbers

Problem: Sum Root to Leaf Numbers

We just use depth-first tree to form a root-to-leaf number at leaf nodes and add them to the answer.

Code in Python:

# 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 sumNumbers(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root: return 0
        self.sum = 0
        def dfs(node, num):
            _num = num*10+node.val
            if node.left: dfs(node.left, _num)
            if node.right: dfs(node.right, _num)
            if not node.left and not node.right: self.sum += _num
        dfs(root, 0)
        return self.sum