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.

参考了别人的答案，发现也不很难。对二叉树的递归定义理解还是不够。

/** * 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) {        return sumCal(root,0);            }        int sumCal(TreeNode * root,int sum)    {        if(root == 0)            return 0;        if(root -> left == 0 && root -> right == 0)            return sum * 10 + root ->val;                    return sumCal(root->left,sum * 10 + root ->val)+sumCal(root->right,sum * 10 + root ->val);    }};