LeetCode | 129. Sum Root to Leaf Numbers

题目：

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.

题意：

同样使用回溯法进行求解。需要注意的是每次的数字是当前路径的表示1->2为12。

代码：

void backSum(TreeNode* root, int cur, int& sum) {
        if(root->left == NULL && root->right == NULL)
        {
            sum += cur*10 + root->val;
            return;
        }
        if(root->left != NULL)
        {
            backSum(root->left, cur*10+root->val, sum);
        }
        if(root->right != NULL)
        {
            backSum(root->right, cur*10+root->val, sum);
        }
        return;
    }
    int sumNumbers(TreeNode* root) {
        if(root == NULL)
            return 0;
        int sum = 0;
        backSum(root, 0, sum);
        return sum;
    }