LeetCode129：Sum Root to Leaf Numbers

題目：

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.

解題思路：

採用DFS，遍歷二叉樹，遇到葉子節點時，進行累加和，不多說，直接上程式碼。

實現程式碼：

#include <iostream>
#include <vector> 

using namespace std;

/*
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.

*/

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 
struct TreeNode {
     int val;
     TreeNode *left;
     TreeNode *right;    
     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

void addNode(TreeNode* &root, int val)
{
    if(root == NULL)
    {
        TreeNode *node = new TreeNode(val);
        root = node;
    }
    else if(root->val < val)
    {
        addNode(root->right, val);
    }
    else if(root->val > val)
    {
        addNode(root->left, val);
    }
}

void printTree(TreeNode *root)
{
    if(root)
    {
        cout<<root->val<<" ";
        printTree(root->left);
        printTree(root->right);
    }
}
class Solution {
public:
    int sumNumbers(TreeNode *root) {
        if(root == NULL)
            return 0;
        int sum = 0;
        vector<int> v;
        dfs(root, v, sum);
        return sum;    
    }

    void dfs(TreeNode *node, vector<int> &v, int &sum)
    {
        if(node == NULL)
            return ;
            
        v.push_back(node->val);
        if(node->left == NULL && node->right == NULL)
        {
            vector<int>::iterator iter;
            int tmp = 0;
            for(iter = v.begin(); iter != v.end(); ++iter)
                tmp =tmp*10 + *iter;
            sum += tmp;
                                           
        }
        else
        {
            if(node->left)
                dfs(node->left, v, sum);
            if(node->right)
                dfs(node->right, v, sum);    
        }
        v.pop_back();
        
    }
};
int main(void)
{
    TreeNode *root = new TreeNode(5);
    addNode(root, 7);
    addNode(root, 3);
    addNode(root, 9);
    addNode(root, 1);
    printTree(root);
    cout<<endl;
    
    Solution solution;
    int sum = solution.sumNumbers(root);
    cout<<sum<<endl;
    return 0;
}