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| // @Title: 二叉树的后序遍历 (Binary Tree Postorder Traversal)
// @Author: 15816537946@163.com
// @Date: 2019-11-25 18:26:28
// @Runtime: 0 ms
// @Memory: 2.1 MB
/*
* @lc app=leetcode.cn id=145 lang=golang
*
* [145] 二叉树的后序遍历
*
* https://leetcode-cn.com/problems/binary-tree-postorder-traversal/description/
*
* algorithms
* Hard (67.10%)
* Likes: 146
* Dislikes: 0
* Total Accepted: 25.5K
* Total Submissions: 38K
* Testcase Example: '[1,null,2,3]'
*
* 给定一个二叉树,返回它的 后序 遍历。
*
* 示例:
*
* 输入: [1,null,2,3]
* 1
* \
* 2
* /
* 3
*
* 输出: [3,2,1]
*
* 进阶: 递归算法很简单,你可以通过迭代算法完成吗?
*
*/
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func postorderTraversal(root *TreeNode) []int {
if root == nil {
return nil
}
res := make([]int, 0)
nodes := make([]*TreeNode, 1, 1024)
nodes[0] = root
for len(nodes) > 0 {
node := nodes[len(nodes)-1]
nodes = nodes[:len(nodes)-1]
res = append(res, node.Val)
if node.Left != nil {
nodes = append(nodes, node.Left)
}
if node.Right != nil {
nodes = append(nodes, node.Right)
}
}
reverse(res)
return res
}
func reverse(arr []int) {
lo, hi :=0, len(arr)-1
for lo < hi {
arr[lo],arr[hi] = arr[hi], arr[lo]
lo++
hi--
}
}
|