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);
    }
};