Itenaries.js

function buildItenary(options, startCity) {
	const citiesMap = new Map()
	options.forEach(([origin, dest]) => {
		if (citiesMap.has(origin)) {
			const stored = citiesMap.get(origin)
			stored.push(dest)
			citiesMap.set(origin, stored)
		} else {
			citiesMap.set(origin, [dest])
		}
	})

	const originNode = new treeNode(startCity)
	const queue = [originNode]

	while (queue.length > 0) {
		const curEl = queue.pop()
		if (citiesMap.has(curEl.val)) {
			citiesMap.get(curEl.val).forEach((val) => {
				if (val === originNode.val) {
					return
				}
				const node = new treeNode(val)
				queue.push(node)
				curEl.children.push(node)
			})
		}
	}

	// do dfs to collect all routes
	const routes = []
	dfs(originNode, routes, [])

	// expect to get back
	// [["Amsterdam", "London", "Minal"], ["Amsterdam", "Berlin"]
	return routes
}

function dfs(node, routes, route) {
	route.push(node.val)
	if (node.children.length === 0) {
		routes.push([...route])
		return
	}
	node.children.forEach((node) => {
		dfs(node, routes, [...route])
	})
}

class treeNode {
	constructor(val) {
		this.val = val
		this.children = []
	}
}

const cities = [
	["Amsterdam", "London"],
	["Berlin", "Amsterdam"],
	["Barcelona", "Berlin"],
	["London", "Milan"],
	["Amsterdam", "Berlin"],
]
console.log(buildItenary(cities, "Amsterdam"))
console.log(buildItenary(cities, "London"))
console.log(buildItenary(cities, "Milan"))