129. Sum Root to Leaf Numbers

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 number123.

Find the total sum of all root-to-leaf numbers.

For example,

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.

解答：

/**

 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int sumNumbers(struct TreeNode* root) {
    int sum=0;
    return num(root,sum);
}

int num(struct TreeNode* root,int sum){
    int temp=0;
    if(root==NULL) return 0;
    sum=sum*10+root->val;
    if(root->left==NULL && root->right==NULL){
        return sum;
    }
    return num(root->left,sum)+num(root->right,sum);
}