[LeetCode]Sum Root to Leaf Numbers

题目描述:(链接)

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.

解题思路:

深度优先搜索，遍历所有根节点到叶节点的路径。

/**
 * 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) {
        return sumNumbers(root, 0);
    }
private:
    int sumNumbers(TreeNode *root, int sum) {
        if (root == nullptr) return 0;
        sum  = sum * 10 + root->val;
        if (root->left == nullptr && root->right == nullptr) {
            return sum;
        }
        
        return sumNumbers(root->left, sum) + sumNumbers(root->right, sum);
    }
};