[leetcode] 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.

递归咯~ 返回条件就是当前节点为叶子节点，结算一下

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {    int ret;public:    void num(TreeNode *root, int x){        int v = x* 10 + root -> val;        if(!root -> left && !root -> right){            ret += v;            return;        }        if(root -> left) num(root -> left, v);        if(root -> right) num(root -> right, v);            }    int sumNumbers(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        ret = 0;                if(!root) return 0;        num(root, 0);        return ret;    }};