Longest Consecutive Sequence

/*
 * Problem : Process an array.
 * Input   : n, then n integers.
 * Output  : The longest length.
 * Approach: Use a set and start only at sequence beginnings.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static int solve(int[] a) {
        // Step 1: Put all numbers in a set. A set finds a number in constant time.
        java.util.Set<Integer> numbers = new java.util.HashSet<>();
        for (int value : a) {
            numbers.add(value);
        }

        int best = 0;
        for (int value : numbers) {
            // Step 2: Only start counting at the beginning of a sequence (value - 1 is missing).
            if (!numbers.contains(value - 1)) {
                int end = value;

                // Step 3: Walk to the right while the next number exists.
                while (numbers.contains(end + 1)) {
                    end++;
                }
                best = Math.max(best, end - value + 1);
            }
        }
        return best;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(solve(a));
    }
}