内存在Java中使用0Kb

Question

我在竞争性编程竞赛期间浏览了一些用Java编写的代码，而我很难理解他们的代码使用的内存为0kb。

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

public class C {
    FastScanner in = new FastScanner(System.in);
    PrintWriter out = new PrintWriter(System.out);

    public void run() {
        int n = in.nextInt(), m = in.nextInt(), k = in.nextInt();
        int[] a = in.nextIntArray(n);

        long[] sum = new long[n+1];
        for (int i = 1; i <= n; i++) {
            sum[i] = sum[i-1] + a[i-1];
        }

        long[] cur = new long[n+1];
        long[] old = new long[n+1];

        for (int i = 1; i <= k; i++) {
            Arrays.fill(cur, Long.MIN_VALUE / 2);
            for (int j = i * m; j <= n; j++) {
                cur[j] = Math.max(cur[j-1], old[j-m] + sum[j] - sum[j-m]);
            }
            long[] temp = cur;
            cur = old;
            old = temp;
        }
        System.out.println(old[n]);
        out.close();
    }

    public static void main(String[] args) {
        new C().run();
    }

    public void mapDebug(int[][] a) {
        System.out.println("--------map display---------");

        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < a[i].length; j++) {
                System.out.printf("%3d ", a[i][j]);
            }
            System.out.println();
        }

        System.out.println("----------------------------");
        System.out.println();
    }

    public void debug(Object... obj) {
        System.out.println(Arrays.deepToString(obj));
    }

    class FastScanner {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public FastScanner(InputStream stream) {
            this.stream = stream;
            //stream = new FileInputStream(new File("dec.in"));

        }

        int read() {
            if (numChars == -1)
                throw new InputMismatchException();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        boolean isEndline(int c) {
            return c == '\n' || c == '\r' || c == -1;
        }

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

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

            return array;
        }

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

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

            return array;
        }

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

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

            return array;
        }

        String next() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

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

            return array;
        }

        String nextLine() {
            int c = read();
            while (isEndline(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndline(c));
            return res.toString();
        }
    }
}

在比赛期间如何使用记忆？在执行时和内存方面，Java可以使用哪些基本优化。 究竟是什么public void debug(Object ... obj)我以前从未见过这样的事情。之前在。“