129.Sum Root to Leaf Numbers

tags: Medium,Tree,DFS

129. Sum Root to Leaf Numbers

題目描述

You are given the root of a binary tree containing digits from 0 to 9 only.

Each root-to-leaf path in the tree represents a number.

• For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.

Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer.

A leaf node is a node with no children.

範例

Example 1:

Input: root = [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: root = [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.

Constraints:

• The number of nodes in the tree is in the range [1, 1000].
• 0 <= Node.val <= 9
• The depth of the tree will not exceed 10.

解答

Python

class Solution:
    def sumNumbers(self, root: Optional[TreeNode]) -> int:
        nums = []

        def dfs(root, num=None):
            if not root: return
            if not num: num = []
            
            num.append(str(root.val))
            if not root.left and not root.right:
                num_str = "".join(num)
                nums.append(int(num_str))

            dfs(root.left, num)
            dfs(root.right, num)

            num.pop()

        dfs(root)
        return sum(nums)

Ron ChenTue, Mar 14, 2023

Reference

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