题目描述：

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.

代码：

int get_number(vector<int> vec)
{
    int length = vec.size();
    int n = 0;
    int factor = 1;
    for(int i = length-1;i >= 0;i--)
    {
        n = n + factor * vec[i];
        factor = factor * 10;
    }
    return n;
}

int calculate(vector<int> vec,TreeNode *treeNode)
{
    if(treeNode->left == NULL && treeNode->right == NULL)
    {
        vec.push_back(treeNode->val);
        return get_number(vec);
    }

    else if(treeNode->left != NULL && treeNode->right == NULL)
    {
        vec.push_back(treeNode->val);
        return calculate(vec,treeNode->left);
    }

    else if(treeNode->left == NULL && treeNode->right != NULL)
    {
        vec.push_back(treeNode->val);
        return calculate(vec,treeNode->right);
    }

    else if(treeNode->left != NULL && treeNode->right != NULL)
    {
        vec.push_back(treeNode->val);
        return calculate(vec,treeNode->left) + calculate(vec,treeNode->right);
    }
}



int Solution::sumNumbers(TreeNode *root)
{

    if（root == NULL）

<span style="white-space:pre">	</span>return 0;

    vector<int> vec;
    return calculate(vec,root);
}

LeetCode:Sum Root to Leaf Numbers