0129. Sum Root to Leaf Numbers

129. Sum Root to Leaf Numbers #

题目 #

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.

Example:

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.

题目大意 #

给定一个二叉树,它的每个结点都存放一个 0-9 的数字,每条从根到叶子节点的路径都代表一个数字。例如,从根到叶子节点路径 1->2->3 代表数字 123。计算从根到叶子节点生成的所有数字之和。说明: 叶子节点是指没有子节点的节点。

解题思路 #

  • 这一题是第 257 题的变形题,第 257 题要求输出每条从根节点到叶子节点的路径,这一题变成了把每一个从根节点到叶子节点的数字都串联起来,再累加每条路径,求出最后的总和。实际做题思路基本没变

代码 #


package leetcode

import (
	"strconv"
)

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumNumbers(root *TreeNode) int {
	res, nums := 0, binaryTreeNums(root)
	for _, n := range nums {
		num, _ := strconv.Atoi(n)
		res += num
	}
	return res
}

func binaryTreeNums(root *TreeNode) []string {
	if root == nil {
		return []string{}
	}
	res := []string{}
	if root.Left == nil && root.Right == nil {
		return []string{strconv.Itoa(root.Val)}
	}
	tmpLeft := binaryTreeNums(root.Left)
	for i := 0; i < len(tmpLeft); i++ {
		res = append(res, strconv.Itoa(root.Val)+tmpLeft[i])
	}
	tmpRight := binaryTreeNums(root.Right)
	for i := 0; i < len(tmpRight); i++ {
		res = append(res, strconv.Itoa(root.Val)+tmpRight[i])
	}
	return res
}


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