LeetCode:129. Sum Root to Leaf Numbers

题目描述

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.

题目大意： 将二叉树的每一条 root-to-leaf 路径看做一个十进制数字，计算所有的路径构成数字的和。

解题思路 —— 深度搜索

深度搜索，在每个叶节点计算到达当前节点路径的数字，并将其加入和中。

AC 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 {
    // 获取 root 的 “Sum Root to Leaf Numbers”, num表示当前root-to-curNode的数字
    int sumNumbersRef(TreeNode* root, int num = 0)
    {
        if(root == nullptr) return 0;

        num = num*10 + root->val;

        if(root->left == nullptr && root->right == nullptr) return num;
        else return sumNumbersRef(root->left, num) + sumNumbersRef(root->right, num);
    }
public:
    int sumNumbers(TreeNode* root) {
        return sumNumbersRef(root);
    }
};