Problem: 2062C - Cirno and Operations
Language: Java 21

Previous submission (verdict: Wrong answer on test 2):
import java.io.*;
import java.util.*;

public class TestCodeforces {
    public static void main(String[] args) {
        IO io = new IO();
        int t = io.nextInt();

        while (t-- > 0) {
            solve(io);
        }
        io.flush();
        io.close();
    }

    public static void solve(IO io) {
        int n = io.nextInt();
        int[] arr = io.nextIntArray(n);
        long ans = Long.MIN_VALUE;
        int now = n;
        for (int k = 0; k < n; k++) {
            // calc sum
            long sum = 0;
            for (int i = 0; i < now; i++)
                sum += arr[i];
            if (k == 0) {
                ans = max(ans, sum);
            } else {
                ans = max(ans, max(sum, -sum));
            }
            for (int i = 0; i < now - 1; i++) {
                arr[i] = arr[i + 1] - arr[i];
            }

            now--;
        }

        System.out.println(ans);
    }

    public static <T extends Comparable<T>> int eq(T a, T b) {
        return (a.compareTo(b) == 0) ? 1 : 0;
    }

    public static <T extends Comparable<T>> T max(T a, T b) {
        return (a.compareTo(b) > 0) ? a : b;
    }

    public static <T extends Comparable<T>> T min(T a, T b) {
        return (a.compareTo(b) < 0) ? a : b;
    }

    static class IO {
        BufferedReader br;
        StringTokenizer st;
        PrintWriter pw;

        public IO() {
            br = new BufferedReader(new InputStreamReader(System.in));
            pw = new PrintWriter(System.out);
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        String[] nextStringArray(int n) {
            String[] arr = new String[n];
            for (int i = 0; i < n; i++) {
                arr[i] = next();
            }
            return arr;
        }

        int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }

        long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }

        double[] nextDoubleArray(int n) {
            double[] arr = new double[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextDouble();
            }
            return arr;
        }

        void print(Object obj) {
            pw.print(obj);
        }

        void println(Object obj) {
            pw.println(obj);
        }

        void flush() {
            pw.flush();
        }

        void close() {
            pw.close();
        }

        public void display(int[] arr) {
            for (int num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(long[] arr) {
            for (long num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(double[] arr) {
            for (double num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(String[] arr) {
            for (String str : arr) {
                pw.print(str + " ");
            }
            pw.println();
        }
    }
}


Submission (verdict: Wrong answer on test 2):
import java.io.*;
import java.util.*;

public class TestCodeforces {
    public static void main(String[] args) {
        IO io = new IO();
        int t = io.nextInt();

        while (t-- > 0) {
            solve(io);
        }
        io.flush();
        io.close();
    }

    public static void solve(IO io) {
        int n = io.nextInt();
        int[] arr = io.nextIntArray(n);
        long ans = Long.MIN_VALUE;
        int now = n;
        for (int k = 0; k < n; k++) {
            // calc sum
            long sum = 0;
            for (int i = 0; i < now; i++)
                sum += arr[i];
            if (k == 0) {
                ans = Math.max(ans, sum);
            } else {
                ans = Math.max(ans, Math.max(sum, -sum));
            }
            for (int i = 0; i < now - 1; i++) {
                arr[i] = arr[i + 1] - arr[i];
            }

            now--;
        }

        System.out.println(ans);
    }

    public static <T extends Comparable<T>> int eq(T a, T b) {
        return (a.compareTo(b) == 0) ? 1 : 0;
    }

    public static <T extends Comparable<T>> T max(T a, T b) {
        return (a.compareTo(b) > 0) ? a : b;
    }

    public static <T extends Comparable<T>> T min(T a, T b) {
        return (a.compareTo(b) < 0) ? a : b;
    }

    static class IO {
        BufferedReader br;
        StringTokenizer st;
        PrintWriter pw;

        public IO() {
            br = new BufferedReader(new InputStreamReader(System.in));
            pw = new PrintWriter(System.out);
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        String[] nextStringArray(int n) {
            String[] arr = new String[n];
            for (int i = 0; i < n; i++) {
                arr[i] = next();
            }
            return arr;
        }

        int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }

        long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }

        double[] nextDoubleArray(int n) {
            double[] arr = new double[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextDouble();
            }
            return arr;
        }

        void print(Object obj) {
            pw.print(obj);
        }

        void println(Object obj) {
            pw.println(obj);
        }

        void flush() {
            pw.flush();
        }

        void close() {
            pw.close();
        }

        public void display(int[] arr) {
            for (int num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(long[] arr) {
            for (long num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(double[] arr) {
            for (double num : arr) {
                pw.print(num + " ");
            }
            pw.println();
        }

        public void display(String[] arr) {
            for (String str : arr) {
                pw.print(str + " ");
            }
            pw.println();
        }
    }
}