﻿ Java - Longest sequence of elements from an unsorted array

# Java: 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 an 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 the HashSet class from the java.util package.
import java.util.HashSet;

// Define a class named Exercise34.
public class Exercise34 {
// The main method for executing the program.
public static void main(String[] args) {
// Declare an array of integers.
int nums[] = {49, 1, 3, 200, 2, 4, 70, 5};

// Print the original array length.
System.out.println("Original array length: " + nums.length);

// Print the elements of the array.
System.out.print("Array elements are: ");
for (int i = 0; i < nums.length; i++) {
System.out.print(nums[i] + " ");
}

// Calculate the new length of the array using the longest_sequence method and print it.
System.out.println("\nThe new length of the array is: " + longest_sequence(nums));
}

// Define a method named longest_sequence that takes an array of integers as input.
public static int longest_sequence(int[] nums) {
// Create a HashSet to store unique values from the input array.
final HashSet h_set = new HashSet();
for (int i : nums) {
}

// Initialize a variable to store the length of the longest sequence.
int longest_sequence_len = 0;

// Iterate through the elements of the input array.
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;
}
// Update the longest sequence length if a longer sequence is found.
longest_sequence_len = Math.max(longest_sequence_len, length);
}

// Return the length of the longest sequence.
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:

Java Code Editor:

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