Java Program to Find the Peak Element of an Array O(n) time (Naive Method)

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This is a Java Program to find peak element of an array. A peak element of an array is that element which is not smaller than its neighbors. Consider only one neighbour for corner elements. The time complexity of the following program is O (n).

Brute Force Algorithm is as follows :

for i in range (n) :
    if A[i - 1] <= A[i] >= A[i + 1] :
        print A[i]
    end if
end for

Here is the source code of the Java program to find peak element of an array. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

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  1. /*
  2.  *    Java Program to Find the peak element of an array O(n) time (Naive Method)
  3.  */
  4.  
  5. import java.util.Scanner;
  6.  
  7. public class PeakElement1
  8. {
  9.     public static void main(String[] args)
  10.     {    
  11.         Scanner scan = new Scanner(System.in);
  12.         System.out.println("Enter size of array");
  13.         int N = scan.nextInt();
  14.         int[] arr = new int[N + 2];
  15.         /* set corner values to -infinity */
  16.         arr[0] = Integer.MIN_VALUE;
  17.         arr[N + 1] = Integer.MIN_VALUE;
  18.  
  19.         /* Accept N elements */
  20.         System.out.println("Enter "+ N +" elements");
  21.         for (int i = 1; i <= N; i++)
  22.             arr[i] = scan.nextInt();
  23.  
  24.         /* Find All Peak Elements */
  25.         System.out.println("\nAll Peak Elements : ");
  26.         for (int i = 1; i <= N; i++)
  27.             if (arr[i - 1] <= arr[i] && arr[i] >= arr[i + 1])
  28.                 System.out.println(arr[i] +" at position "+ i);
  29.  
  30.         System.out.println();    
  31.     }         
  32. }

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Enter size of array
6
Enter 6 elements
1 2 5 5 4 1
 
All Peak Elements :
5 at position 3
5 at position 4
 
 
 
Enter size of array
7
Enter 7 elements
6 24 15 2 23 99 67
 
All Peak Elements :
24 at position 2
99 at position 6
 
 
 
Enter size of array
10
Enter 10 elements
10 9 8 24 8 7 97 28 17 63
 
All Peak Elements :
10 at position 1
24 at position 4
97 at position 7
63 at position 10

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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