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 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.

思路：这道题使用递归。这道题思路比较明确，目标是把从根到叶子节点的所有路径得到的整数累加起来，递归条件即是把当前的sum*10加上当前结点的值传入函数，进行递归，最终把左右子树的总和相加。结束条件就是如果一个结点是叶子结点，那么我们应该累加到结果总和中。

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int sumPath(TreeNode *root,int sum)

    {

        if(root==NULL)

            return 0;

        sum=sum*10+root->val;

        if(root->left==NULL&&root->right==NULL)

        {

            return sum;

        }

        if(root->left==NULL)

            return sumPath(root->right,sum);

        if(root->right==NULL)

            return sumPath(root->left,sum);

        return sumPath(root->left,sum)+sumPath(root->right,sum);

    }

    int sumNumbers(TreeNode *root) {

        int sum=0;

        return sumPath(root,sum);

    }

};