Merge pull request neetcode-gh#1659 from a93a/355

Create 0355-design-twitter.kt

kotlin/0355-design-twitter.kt

@@ -0,0 +1,63 @@
+class Twitter() {
+
+ var time = 0
+ val tweetMap = HashMap<Int, ArrayList<Pair<Int, Int>>>() //[userId, [time, tweetId]]
+ val followMap = HashMap<Int, HashSet<Int>>() //[userId, [userId]] hashset to avoud duplicats
+
+ fun postTweet(userId: Int, tweetId: Int) {
+ val tweetList = tweetMap.getOrDefault(userId, ArrayList<Pair<Int, Int>>())
+ tweetList.add(time to tweetId)
+ tweetMap.put(userId, tweetList)
+ time++
+ }
+
+ fun getNewsFeed(userId: Int): List<Int> {
+ val res = ArrayList<Int>()
+ val maxHeap = PriorityQueue<IntArray>{ a,b -> b[0] - a[0] } //[time, tweetId, index, uID] maxHeap with latest (highest time) first
+
+ val fl = followMap.getOrDefault(userId, HashSet<Int>())
+ fl.add(userId) // get our own tweets aswell
+ for(friend in fl){
+ val tl = tweetMap.get(friend)
+ if(tl != null){
+ var index = tl.size-1
+ val (time, tweetId) = tl.get(index)
+ maxHeap.add(intArrayOf(time, tweetId, --index, friend))
+ }
+ }
+ while(res.size < 10 && !maxHeap.isEmpty()){
+ val (t, tw, i, f) = maxHeap.poll()
+ res.add(tw)
+ val tl = tweetMap.get(f)
+ if(tl != null && tl.size > 0 && i >= 0){
+ val (time, tweetId) = tl.get(i)
+ maxHeap.add(intArrayOf(time, tweetId, i-1, f))
+ } 
+ }
+ return res
+ }
+
+ fun follow(followerId: Int, followeeId: Int) {
+ val followSet = followMap.getOrDefault(followerId, HashSet<Int>())
+ followSet.add(followeeId)
+ followMap.put(followerId, followSet)
+ }
+
+ fun unfollow(followerId: Int, followeeId: Int) {
+ val followSet = followMap.getOrDefault(followerId, HashSet<Int>())
+ followSet?: return
+ if(followSet.contains(followeeId)){
+ followSet.remove(followeeId)
+ followMap.put(followerId, followSet)
+ }
+ }
+}
+
+/**
+ * Your Twitter object will be instantiated and called as such:
+ * var obj = Twitter()
+ * obj.postTweet(userId,tweetId)
+ * var param_2 = obj.getNewsFeed(userId)
+ * obj.follow(followerId,followeeId)
+ * obj.unfollow(followerId,followeeId)
+ */