[Leetcode]Sum Root to Leaf Numbers

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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.

用递归方法~把当前的和乘以10并加上当前节点的值传入下一函数，进行递归，最后把左右子树的总和相加；结束条件就是：如果是叶节点，那么应该累加到结果总和中，如果是空节点，则直接返回0~代码如下~

class Solution:    # @param root, a tree node    # @return an integer    def sumNumbers(self, root):        return self.helper(root, 0)            def helper(self, root, sumVal):        if root is None: return 0        if not root.left and not root.right:            return (sumVal * 10 + root.val)        return self.helper(root.left, sumVal * 10 + root.val) + self.helper(root.right, sumVal * 10 + root.val)

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