18:T59d,import java.util.* // Design a simplified Twitter with post, follow, unfollow, and news feed. // // Think about: How to efficiently retrieve the 10 most recent tweets? // Hint: Consider using a heap to merge sorted tweet lists. // // Example: // postTweet(1, 5) // getNewsFeed(1) → [5] // follow(1, 2) // postTweet(2, 6) // getNewsFeed(1) → [6, 5] (most recent first) class Twitter { fun postTweet(userId: Int, tweetId: Int) { } fun getNewsFeed(userId: Int): List { return emptyList() } fun follow(followerId: Int, followeeId: Int) { } fun unfollow(followerId: Int, followeeId: Int) { } } fun runTwitterScript(commands: List, args: List>): String { var twitter: Twitter? = null val results = mutableListOf>() commands.forEachIndexed { i, cmd -> val a = args[i] when (cmd) { "Twitter" -> twitter = Twitter() "postTweet" -> twitter!!.postTweet((a[0] as Number).toInt(), (a[1] as Number).toInt()) "getNewsFeed" -> results.add(twitter!!.getNewsFeed((a[0] as Number).toInt())) "follow" -> twitter!!.follow((a[0] as Number).toInt(), (a[1] as Number).toInt()) "unfollow" -> twitter!!.unfollow((a[0] as Number).toInt(), (a[1] as Number).toInt()) } } return "[" + results.joinToString(", ") { list -> "[" + list.joinToString(", ") + "]" } + "]" }19:T7cc,import java.util.* class Twitter { private val tweets = mutableMapOf>>() // userId -> [(timestamp, tweetId)] private val following = mutableMapOf>() // userId -> followeeIds private var timestamp = 0 fun postTweet(userId: Int, tweetId: Int) { tweets.getOrPut(userId) { mutableListOf() }.add(Pair(timestamp, tweetId)) timestamp++ } fun getNewsFeed(userId: Int): List { val feed = mutableListOf>() // Add user's own tweets tweets[userId]?.let {

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