145. Binary Tree Postorder Traversal

题目

Given a binary tree, return the postorder traversal of its nodes' values.

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [3,2,1]

Follow up: Recursive solution is trivial, could you do it iteratively?

题目大意

后根遍历一颗树。

解题思路

递归的实现方法，见代码。

代码

package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func postorderTraversal(root *TreeNode) []int {
	var result []int
	postorder(root, &result)
	return result
}

func postorder(root *TreeNode, output *[]int) {
	if root != nil {
		postorder(root.Left, output)
		postorder(root.Right, output)
		*output = append(*output, root.Val)
	}
}

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