Java Program to Find ith Largest Number from a Given List Using Order-Statistic Algorithm

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This is a java program to find the ith largest element from a list using order-statistic algorithm. This version of the code uses quick sort partitioning technique.

Here is the source code of the Java Program to Find ith Largest Number from a Given List Using Order-Statistic Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1.  
  2. package com.sanfoundry.combinatorial;
  3.  
  4. import java.util.Scanner;
  5.  
  6. public class KthLargestOrderStatistics
  7. {
  8.     public static int partition(int[] array, int first, int last)
  9.     {
  10.         int pivot = array[first];
  11.         int pivotPosition = first++;
  12.         while (first <= last)
  13.         {
  14.             // scan for values less than the pivot
  15.             while ((first <= last) && (array[first] < pivot))
  16.             {
  17.                 first++;
  18.             }
  19.             // scan for values greater than the pivot
  20.             while ((last >= first) && (array[last] >= pivot))
  21.             {
  22.                 last--;
  23.             }
  24.             if (first > last)
  25.             {
  26.                 // swap the last uncoformed
  27.                 // element with the pivot
  28.                 swap(array, pivotPosition, last);
  29.             }
  30.             else
  31.             {
  32.                 // swap unconformed elements:
  33.                 // first that was not lesser than the pivot
  34.                 // and last that was not larger than the pivot
  35.                 swap(array, first, last);
  36.             }
  37.         }
  38.         return last;
  39.     }
  40.  
  41.     private static void swap(int[] array, int first, int last)
  42.     {
  43.         int temp;
  44.         temp = array[first];
  45.         array[first] = array[last];
  46.         array[last] = temp;
  47.     }
  48.  
  49.     public static int orderStatistic(int[] array, int k, int first, int last)
  50.     {
  51.         int pivotPosition = partition(array, first, last);
  52.         if (pivotPosition == k - 1)
  53.         {
  54.             return array[k - 1];
  55.         }
  56.         if (k - 1 < pivotPosition)
  57.         {
  58.             return orderStatistics(array, k, first, pivotPosition - 1);
  59.         }
  60.         else
  61.         {
  62.             return orderStatistics(array, k, pivotPosition + 1, last);
  63.         }
  64.     }
  65.  
  66.     // iterative version
  67.     private static int orderStatistics(int[] array, int k, int first, int last)
  68.     {
  69.         int pivotPosition = partition(array, first, last);
  70.         while (pivotPosition != k - 1)
  71.         {
  72.             if (k - 1 < pivotPosition)
  73.             {
  74.                 last = pivotPosition - 1;
  75.             }
  76.             else
  77.             {
  78.                 first = pivotPosition + 1;
  79.             }
  80.             pivotPosition = partition(array, first, last);
  81.         }
  82.         return array[k - 1];
  83.     }
  84.  
  85.     public static int kthSmallest(int[] array, int k)
  86.     {
  87.         return orderStatistic(array, k, 0, array.length - 1);
  88.     }
  89.  
  90.     public static int kthLargest(int[] array, int k)
  91.     {
  92.         return orderStatistic(array, array.length - k + 1, 0, array.length - 1);
  93.     }
  94.  
  95.     public static void main(String[] args)
  96.     {
  97.         Scanner sc = new Scanner(System.in);
  98.         System.out.println("Enter the number of elements in the sequence: ");
  99.         int n = sc.nextInt();
  100.         int[] sequence = new int[n];
  101.         System.out.println("Enter the elements of the sequence: ");
  102.         for (int i = 0; i < sequence.length; i++)
  103.         {
  104.             sequence[i] = sc.nextInt();
  105.         }
  106.         System.out
  107.                 .println("Enter the kth index to be returned as kth largest element of the sequence:");
  108.         int k = sc.nextInt();
  109.         System.out.println("Kth largest:" + kthLargest(sequence, k));
  110.         sc.close();
  111.     }
  112. }

Output:

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$ javac KthLargestOrderStatistics.java
$ java KthLargestOrderStatistics
 
Enter the number of elements in the sequence: 
10
Enter the elements of the sequence: 
2 5 6 7 4 7 9 5 8 1
Enter the kth index to be returned as kth largest element of the sequence:
4
Kth largest:7

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter