Java Array Exercises: Find the length of the longest consecutive elements sequence from a given unsorted array of integers

Java Array: Exercise-34 with Solution

Write a Java program to find the length of the longest consecutive elements sequence from a given unsorted array of integers.
Sample array: [49, 1, 3, 200, 2, 4, 70, 5]
The longest consecutive elements sequence is [1, 2, 3, 4, 5], therefore the program will return its length 5.

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.HashSet;
public class Exercise34 {    
   public static void main(String[] args) {
        int nums[] = {49, 1, 3, 200, 2, 4, 70, 5};  
		System.out.println("Original array length: "+nums.length);
		System.out.print("Array elements are: ");
       for (int i = 0; i < nums.length; i++)
        {
            System.out.print(nums[i]+" ");
        }
		System.out.println("\nThe new length of the array is: "+longest_sequence(nums));
			
    }
    
    public static int longest_sequence(int[] nums) {
      final HashSet<Integer> h_set = new HashSet<Integer>();
        for (int i : nums) h_set.add(i);

        int longest_sequence_len = 0;
        for (int i : nums) {
            int length = 1;
            for (int j = i - 1; h_set.contains(j); --j) {
                h_set.remove(j);
                ++length;
            }
            for (int j = i + 1; h_set.contains(j); ++j) {
                h_set.remove(j);
                ++length;
            }
            longest_sequence_len = Math.max(longest_sequence_len, length);
        }
        return longest_sequence_len;
    }
}

Sample Output:

                                                                              
Original array length: 8                                               
Array elements are: 49 1 3 200 2 4 70 5                                
The new length of the array is: 5

Flowchart:

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Java Code Editor:

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