Java TestCase Generator + Answer Comparator for ProblemSolving

TestcaseGenerator.java

/**
 * Java TestCase Generator + Answer Comparator for ProblemSolving
 * @author sinam7 (muwon777@naver.com)
 * <p>
 * To use this generator, You need two java file first:
 *  1. Code you wrote -> default: in class Main
 *  2. AC Code -> default: in class Solution
 *  (!) the code must use stdio (System.in, System.out)
 * <p>
 * Then, make your code's System.in to our custom InputStreamReader.
 * @see Line 50~58
 * <p>
 * Change the code inside these methods below:
 *  1. private static void generateTestCase() -> write a code to generate testcase.
 *  2. private static void runCorrectCode(InputStreamReader in) -> to run correct code's psvm.
 *  3. private static void runTestCode(InputStreamReader in) -> to run test code's psvm.
 */

import java.io.*;
import java.util.StringTokenizer;

public class TestcaseGenerator {
    private static void generateTestCase() {
        /*
        Example: 2 <= N <= 1000000, 1 <= M <= N, Input: "N M"
        for (int i = 2; i <= 1000000; i++) {
            for (int j = 1; j <= i; j++) {
                // run code with string input.
                // if you want to find the first WA testcase, code it like below.
                // WA will return false, AC will return true.
                // else, remove if statement.
                if (!start(i + " " + j + "\n")){
                    return;
                }
            }
        }
         */

        // Code below...
        for (int i = 2; i <= 1000000; i++) {
            for (int j = 1; j <= i; j++) {
                if (!start(i + " " + j + "\n")){
                    return;
                }
            }
        }
        // Code above...
    }

    private static void runCorrectCode(InputStreamReader in) throws IOException {
        Solution.sc.init(in); // Change code if needed -> Change InputStream from 'System.in' to parameter 'in'
        Solution.solve();   // your psvm here
    }

    private static void runTestCode(InputStreamReader in) throws IOException {
        Main.sc.init(in); // Change code if needed -> Change InputStream from 'System.in' to parameter 'in'
        Main.solve();   // your psvm here
    }

    /*
     * Example of sc inner static class.
     */
    @SuppressWarnings("unused")
    static class sc {
        private static BufferedReader br;
        private static StringTokenizer st;

        static void init(InputStreamReader in) {
            br = new BufferedReader(in);
            st = new StringTokenizer("");
        }

        static String next() {
            while (!st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException ignored) {
                }
            }
            return st.nextToken();
        }

        static int nextInt() {
            return Integer.parseInt(next());
        }

    }
    public static void main(String[] args) throws IOException {
        generateTestCase();
    }

    public static boolean start(String tc) {
        final PrintStream defaultSysout = System.out;
        InputStreamReader in1 = new InputStreamReader(new ByteArrayInputStream(tc.getBytes()));
        InputStreamReader in2 = new InputStreamReader(new ByteArrayInputStream(tc.getBytes()));

        String correctOutput = run(() -> {
            try {
                runCorrectCode(in1);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        });
        String testOutput = run(() -> {
            try {
                runTestCode(in2);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        });

        // customize here if you want file output.
        System.setOut(defaultSysout);
        if (!correctOutput.equals(testOutput)) {
            System.out.println("====================");
            System.out.println("Found Wrong result");
            System.out.println("Input:");
            System.out.println(tc);
            System.out.println("Correct Output:");
            System.out.println(correctOutput);
            System.out.println("Test Output:");
            System.out.println(testOutput);
            return false;
        }
        return true;
    }

    private static String run(Runnable runnable) {
        CustomOutputStream outputStream = setUp();
        runnable.run();
        return outputStream.toString();
    }

    private static CustomOutputStream setUp() {
        CustomOutputStream outputStream = new CustomOutputStream();
        PrintStream printStream = new PrintStream(outputStream);
        System.setOut(printStream);
        return outputStream;
    }

    private static class CustomOutputStream extends OutputStream {

        private StringBuilder string = new StringBuilder();

        @Override
        public void write(int b) {
            this.string.append((char) b);
        }

        @Override
        public String toString() {
            return this.string.toString();
        }
    }

}