129. Sum Root to Leaf Numbers

Leetcode 链接

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.

题意解析

求根节点到叶子节点的所有路劲的和。需要注意的是：一条路径代表一个数值。

解决方案

• 简单路径遍历即可

Go 代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumNumbers(root *TreeNode) int {
    sum := 0
    helper(root, 0, &sum)
    return sum
}

func helper(root *TreeNode, currentSum int, sum *int) {
    if root == nil {
        return
    }

    currentSum = currentSum*10 + root.Val
    if root.Left == nil && root.Right == nil {
        *sum += currentSum
        return
    }

    helper(root.Left, currentSum, sum)
    helper(root.Right, currentSum, sum)
}