LeetCode in Kotlin
145. Binary Tree Postorder Traversal
Easy
Given the root of a binary tree, return the postorder traversal of its nodes’ values.
Example 1:
Input: root = [1,null,2,3]
Output: [3,2,1]
Example 2:
Input: root = []
Output: []
Example 3:
Input: root = [1]
Output: [1]
Constraints:
- The number of the nodes in the tree is in the range
[0, 100]. -100 <= Node.val <= 100
Follow up: Recursive solution is trivial, could you do it iteratively?
Solution
import com_github_leetcode.TreeNode
/*
* Example:
* var ti = TreeNode(5)
* var v = ti.`val`
* Definition for a binary tree node.
* class TreeNode(var `val`: Int) {
* var left: TreeNode? = null
* var right: TreeNode? = null
* }
*/
class Solution {
fun postorderTraversal(root: TreeNode?): MutableList<Int> {
if (root == null) {
return ArrayList()
}
val res = postorderTraversal(root.left)
res.addAll(postorderTraversal(root.right))
res.add(root.`val`)
return res
}
}