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.

分析

从根到叶组成一系列的数，求之和。树的问题最好还是使用递归，到叶子节点时候计算总和跳出循环，如果有左右节点，依次计算之后返回总的和。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int sum(struct TreeNode *root ,int temp,int answer)
{
    if(root==NULL)return 0;
    temp=temp*10+root->val;
    if(root->left==NULL&&root->right==NULL)
    {
        answer+=temp;
        return answer;
    }
    if(root->left!=NULL)
        answer=sum(root->left,temp,answer);
    if(root->right!=NULL)
        answer=sum(root->right,temp,answer);
    return answer;
}
int sumNumbers(struct TreeNode* root) {
    return sum(root,0,0);
}