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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:

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

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:

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

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Java Code Editor:

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Previous: Write a Java program to remove the duplicate elements of a given array and return the new length of the array.
Next: Write a Java program to find the sum of the two elements of a given array which is equal to a given integer.

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Java: Tips of the Day

Different between parseInt() and valueOf() in java?

Well, the API for Integer.valueOf(String) does indeed say that the String is interpreted exactly as if it were given to Integer.parseInt(String). However, valueOf(String) returns a new Integer() object whereas parseInt(String) returns a primitive int.

If you want to enjoy the potential caching benefits of Integer.valueOf(int), you could also use this eyesore:

Integer k = Integer.valueOf(Integer.parseInt("123"))

Now, if what you want is the object and not the primitive, then using valueOf(String) may be more attractive than making a new object out of parseInt(String) because the former is consistently present across Integer, Long, Double, etc.

Ref: https://bit.ly/3vRuIPY