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.

如果要记住上一次结果，要么backtracking,要么加个参数。。。

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int sumNumbers(TreeNode* root) {        if (!root)            return 0;        return helper(root,0);    }    int helper(TreeNode* root, int sum){        if (!root)            return 0;        if (!root->left && !root->right)            return sum*10+root->val;        return helper(root->left,sum*10+root->val)+helper(root->right,sum*10+root->val);    }};

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