[leetcode]129. Sum Root to Leaf Numbers

Analysis

还没工作就想退休—— [每天刷题并不难0.0]

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.
Note: A leaf is a node with no children.

Explanation:

看到树，递归就完事了！

Implement

/**
 * 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) {
        if(!root)
            return 0;
        helper(root, 0);
        return sum;
    }
    void helper(TreeNode* node, int tmp){
        if(!node->left && !node->right){
            tmp = tmp*10+node->val;
            sum += tmp;
        }
        else{
            tmp = tmp*10+node->val;
            if(node->left)
                helper(node->left, tmp);
            if(node->right)
                helper(node->right, tmp);
        }
    }
private:
    int sum = 0;
};