【LeetCode】83. Sum Root to Leaf Numbers

题目描述(Medium)

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.

题目链接

https://leetcode.com/problems/sum-root-to-leaf-numbers/description/

Example 1:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

算法分析

记录当前值和总和，及叶子节点的判断。

提交代码：

/**
 * 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) {
        int total = 0;
        sumNumbers(root, total, 0);
        return total;
    }
    
    void sumNumbers(TreeNode* root, int &total, int curr) {
        if (!root) return;
        
        curr = 10 * curr + root->val;
        if (root->left == NULL && root->right == NULL)
            total += curr;
        
        sumNumbers(root->left, total, curr);
        sumNumbers(root->right, total, curr);
    }
};