Leetcode: Sum Root to Leaf Numbers

Question

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

1

/ \
2 3
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

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Analysis

think of each subtree as a new tree.

Solution

Pass at the first time

# 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 """

        total = 0

        if root==None:
            return total

        return self.helper(root, root.val, total)


    def helper(self, curnode, up2value, total):
        if curnode.left==None and curnode.right==None:
            return total + up2value


        if curnode.left!=None:
            total = self.helper(curnode.left, up2value*10+curnode.left.val, total)
        if curnode.right!=None:
            total = self.helper(curnode.right, up2value*10+curnode.right.val, total)

        return total