Leetcode: Binary Tree Preorder Traversal in Kotlin

144. Binary Tree Preorder Traversal

Given the root of a binary tree, return the preorder traversal of its nodes’ values.

Solution

Traverse the tree in pre-order using DFS.

class Solution {
    fun preorderTraversal(root: TreeNode?): List<Int> = if (root == null) listOf()
    else listOf(root.`val`).plus(preorderTraversal(root.left)).plus(preorderTraversal(root.right))

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