LeetCode | Sum Root to Leaf Numbers

题目：

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：

没什么好说的，还是递归。

代码：

/** * 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 sumNumbers(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(root == NULL)        {            return 0;        }        return num(root, 0);    }        int num(TreeNode * p, int n)    {        if(p->left == NULL && p->right == NULL)        {            return 10 * n + p->val;        }        else if(p -> left == NULL)        {            return num(p->right, 10 * n + p->val);        }        else if(p -> right == NULL)        {            return num(p->left, 10 * n + p->val);        }        else        {            return num(p->left, 10 * n + p->val) + num(p->right, 10 * n + p->val);        }    }};