Longest Arithmetic Progression Algorithm in Java

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This is a Java Program to implement Longest Arithmetic Progression Algorithm. This program finds the length of longest arithmetic progression from an array of numbers.

Here is the source code of the Java Program to implement Longest Arithmetic Progression Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1. /**
  2.  **    Java Program to implement Longest Arithmetic Progression Algorithm
  3.  **/
  4.  
  5. import java.util.Scanner;
  6.  
  7. /** Class  LongestArithmeticProgression **/
  8. public class  LongestArithmeticProgression
  9. {    
  10.     /** function lap **/
  11.     public int lap(int[] A)
  12.     {        
  13.         int n = A.length;
  14.         if (n == 1)
  15.         	return 1;
  16.         int[][] L = new int[n + 1][n + 1];
  17.         int maxLen = 2;
  18.         for (int j = n - 1; j >= 0; j--)
  19.         {
  20.             int i = j - 1, k = j + 1;
  21.             while (i >= 0 && k < n)
  22.             {
  23.                 if (A[i] + A[k] < 2 * A[j])
  24.                     k = k + 1;
  25.                 else if (A[i] + A[k] > 2 * A[j])
  26.                 {
  27.                     L[i][j] = 2;
  28.                     i = i - 1;
  29.                 }
  30.                 else 
  31.                 {
  32.                     L[i][j] = L[j][k] + 1;
  33.                     maxLen = Math.max(maxLen, L[i][j]);
  34.                     i = i - 1;
  35.                     k = k + 1;
  36.                 }
  37.             }
  38.             while (i >= 0)  
  39.             {
  40.                 L[i][j] = 2;
  41.                 i = i - 1;
  42.             }
  43.         }           
  44.         return maxLen;                    
  45.     }
  46.  
  47.     /** Main Function **/
  48.     public static void main(String[] args) 
  49.     {    
  50.         Scanner scan = new Scanner(System.in);
  51.         System.out.println("Longest Arithmetic Progression Algorithm Test\n");
  52.  
  53.         System.out.println("Enter number of elements");
  54.         int n = scan.nextInt();
  55.         int[] arr = new int[n];
  56.         System.out.println("\nEnter "+ n +" elements");
  57.         for (int i = 0; i < n; i++)
  58.             arr[i] = scan.nextInt();
  59.  
  60.         LongestArithmeticProgression obj = new LongestArithmeticProgression(); 
  61.         int result = obj.lap(arr);       
  62.  
  63.         /** print result **/ 
  64.  
  65.         System.out.println("\nLength of Longest Arithmetic Progression : "+ result);        
  66.     }
  67. }

Longest Arithmetic Progression Algorithm Test
 
Enter number of elements
10
 
Enter 10 elements
1 3 7 13 14 15 19 20 25 30
 
Length of Longest Arithmetic Progression : 5
 
 
 
 
Longest Arithmetic Progression Algorithm Test
 
Enter number of elements
10
 
Enter 10 elements
1 2 3 4 5 6 7 8 9 10
 
Length of Longest Arithmetic Progression : 10

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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