Leetcode: Sum Root to Leaf Numbers
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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 = Noneclass 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
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