leetcode 129. Sum Root to Leaf Numbers

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本文介绍了一种算法，用于计算二叉树中所有从根节点到叶子节点的路径所代表数字的总和。通过递归遍历的方式，将每个路径上的数值累加并返回最终的总和。

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.

将上面的值往下面传递

/**
 * 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 sumNumbers(TreeNode* root) 
    {
        ret = 0;   
        if (root)
            count(0, root);
        return ret;   
    }
private:
    int ret;
    void count(int last, TreeNode* root)
    {
        if (!root->left && !root->right) 
            ret += last * 10 + root->val;
       
        if (root->left)
            count(last * 10 + root->val, root->left);
        if (root->right)
            count(last * 10 + root->val, root->right);    
    }
};