leetcode 129：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.

题意：每条路径（从根到叶子结点）相加和

如果是叶子结点，直接返回值

如果不是，选择可走的路走下去（只有左右两条路，ret设置成0，ret最多就是左边路径加右边路径）

dfs中参数val是当前结点位置的路径值

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int dfs(TreeNode* root,int val){        int ret=0;        //叶子结点        if(root->left==NULL&&root->right==NULL)            return val;        //非叶子结点，有些没有的路径是要舍弃的        if(root->left!=NULL) {               ret+=dfs(root->left,val*10+root->left->val);        }        if(root->right!=NULL)            ret+=dfs(root->right,val*10+root->right->val);        return ret;    }    int sumNumbers(TreeNode* root) {        int ret=0;        if(root==NULL)            return ret;        return dfs(root,root->val);    }};