A simple TypeScript functions to show how the trees data structues are implemented

trees.ts

function walkPreTree(curr: BinaryNode<number> | undefined, path: number[]): number[] {
	if (!curr) return path
	path.push(curr.value)
	walkPreTree(curr.left, path)
	walkPreTree(curr.right, path)
	return path
}

function walkInTree(curr: BinaryNode<number> | undefined, path: number[]): number[] {
	if (!curr) return path
	walkInTree(curr.left, path)
	path.push(curr.value)
	walkInTree(curr.right, path)
	return path
}

function walkPostTree(curr: BinaryNode<number> | undefined, path: number[]): number[] {
	if (!curr) return path
	walkInTree(curr.left, path)
	walkInTree(curr.right, path)
	path.push(curr.value)
	return path
}

export function preOrderSearch(head: BinaryNode<number>): number[] {
	return walkPreTree(head, [])
}

type BinaryNode<T> = {
    value: T
    left: BinaryNode<T> | null
    right: BinaryNode<T> | null
}

export function inOrderSearch(head: BinaryNode<number>): number[] {
    return walkInTree(head, [])
}

export function postOrderSearch(head: BinaryNode<number>): number[] {
    return walkPostTree(head, [])
}