Bit Set Class

/*
 * Problem : Process lines.
 * Input   : Several command lines.
 * Output  : One result per command.
 * Approach: Bits in 32-bit words.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Step 1: 1024 flags need 32 words of 32 bits. Flag i lives in word i / 32 at bit i % 32.
        static class BitSet {
            private final int[] words = new int[32];

            void set(int i) {
                words[i >> 5] |= 1 << (i & 31);
            }

            void clear(int i) {
                words[i >> 5] &= ~(1 << (i & 31));
            }

            // Step 2: XOR with the mask turns the bit over: on becomes off and off becomes on.
            void flip(int i) {
                words[i >> 5] ^= 1 << (i & 31);
            }

            int get(int i) {
                return (words[i >> 5] >>> (i & 31)) & 1;
            }

            int count() {
                int total = 0;
                for (int word : words) {
                    total += Integer.bitCount(word);
                }
                return total;
            }
        }

    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(String[] lines) {
        BitSet bits = new BitSet();
        String[] output = new String[lines.length];
        for (int i = 0; i < lines.length; i++) {
            String[] part = lines[i].split(" ");
            if (part[0].equals("COUNT")) {
                output[i] = String.valueOf(bits.count());
            } else if (part[0].equals("GET")) {
                output[i] = String.valueOf(bits.get(Integer.parseInt(part[1])));
            } else {
                int index = Integer.parseInt(part[1]);
                if (part[0].equals("SET")) {
                    bits.set(index);
                } else if (part[0].equals("CLEAR")) {
                    bits.clear(index);
                } else {
                    bits.flip(index);
                }
                output[i] = "ok";
            }
        }
        return output;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        java.util.List<String> all = new java.util.ArrayList<>();
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine().trim();
            if (!line.isEmpty()) {
                all.add(line);
            }
        }
        String[] lines = all.toArray(new String[0]);
        System.out.println(String.join("\n", solve(lines)));
    }
}