Create K Largest Elements

Author: akshayavb99

Course 2 - Data Structures in JAVA/Lecture 21 - Priority Queues II/K Largest Elements

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+/*
+You are given with an integer k and an array of integers that contain numbers in random order. Write a program to find k largest numbers from given array. 
+You need to save them in an array and return it.
+Time complexity should be O(nlogk) and space complexity should be not more than O(k).
+Order of elements in the output is not important.
+
+Input Format :
+Line 1 : Size of array (n)
+Line 2 : Array elements (separated by space)
+Line 3 : Integer k
+
+Output Format :
+k largest elements
+
+Sample Input :
+13
+2 12 9 16 10 5 3 20 25 11 1 8 6 
+4
+Sample Output :
+12
+16
+20
+25
+*/
+
+import java.util.ArrayList;
+import java.util.PriorityQueue;
+public class Solution {
+
+	public static ArrayList<Integer> kLargest(int input[], int k) {
+		/* Your class should be named Solution
+		* Don't write main().
+		* Don't read input, it is passed as function argument.
+		* Return output and don't print it.
+		* Taking input and printing output is handled automatically.
+		*/
+        PriorityQueue<Integer> pq = new PriorityQueue<Integer>();
+        for(int i=0;i<k;i++)
+        {
+            pq.add(input[i]);
+        }
+        
+        for(int i=k;i<input.length;i++)
+        {
+            int minVal=pq.peek();
+            if(minVal<input[i])
+                minVal=input[i];
+            if(minVal!=pq.peek())
+            {
+                pq.poll();
+                pq.add(minVal);
+            }
+        }
+        ArrayList<Integer> arr = new ArrayList<Integer>();
+        while(!pq.isEmpty())
+            arr.add(pq.poll());
+        return arr;
+		
+	}
+}