Leetcode Sum Root to Leaf Numbers

class Solution {
private:
    int sum;
public:
    int sumNumbers(TreeNode *root) {
        sum = 0;
        dfs(root, 0);
        return sum;
    }
    
    void dfs(TreeNode* root, int cur) {
        if (root == NULL) return;
        
        cur = cur * 10 + root->val;
        
        if (root->left == NULL && root->right == NULL) {
            sum += cur;
            return;
        }
        
        dfs(root->left, cur);
        dfs(root->right, cur);
    }
};

水一发

第二轮：

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) {}
 * };
 */
class Solution {
private:
    int total;
public:
    int sumNumbers(TreeNode *root) {
        total = 0;
        dfs(root, 0);
        return total;
    }
    
    void dfs(TreeNode* root, int value) {
        if (root == NULL) {
            return;
        }
        if (root->left == NULL && root->right == NULL) {
            total += value*10 + root->val;
            return;
        }
        dfs(root->left, value * 10 + root->val);
        dfs(root->right, value * 10 + root->val);
    }
};