Merge pull request neetcode-gh#1658 from a93a/621

Create 621-Task-Scheduler.kt

kotlin/621-Task-Scheduler.kt

@@ -0,0 +1,28 @@
+class Solution {
+    fun leastInterval(tasks: CharArray, n: Int): Int {
+        if(n == 0)
+            return tasks.size
+        val hm = HashMap<Char,Int>()
+        for(task in tasks)
+            hm[task] = hm.getOrDefault(task, 0) + 1        
+        val maxHeap = PriorityQueue<Int>(compareBy{-it})
+        for(count in hm.values)
+             maxHeap.add(count) 
+        val q = ArrayDeque<Pair<Int,Int>>() // time, value
+        var time = 0
+        while(!maxHeap.isEmpty() || !q.isEmpty()){
+            if(!maxHeap.isEmpty()){
+                var current = maxHeap.poll()
+                current--
+                if(current > 0)
+                    q.add(Pair(time+n,current))
+            }
+            if(!q.isEmpty()){
+                if(q.peek().first == time)
+                    maxHeap.add(q.poll().second)
+            }
+            time++
+        }    
+        return time          
+    }
+}