1. A 2500-block is 2500 consecutive lines. Read in the input one line at a time, as a sequence of some number of 2500 blocks. Now output these blocks in the opposite order from which they were read, but within each block output the lines in the order in which they were read.

import java.io.BufferedReader; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.util.List; import java.util.ArrayList; public class Part2 { /** * Your code goes here - see Part0 for an example * @param r the reader to read from * @param w the writer to write to * @throws IOException */ public static void doIt(BufferedReader r, PrintWriter w) throws IOException {  // TODO: Your code goes here - see Part0 for an example  } /** * The driver. Open a BufferedReader and a PrintWriter, either from System.in * and System.out or from filenames specified on the command line, then call doIt. * @param args */ public static void main(String[] args) { try { BufferedReader r; PrintWriter w; if (args.length == 0) { r = new BufferedReader(new InputStreamReader(System.in)); w = new PrintWriter(System.out); } else if (args.length == 1) { r = new BufferedReader(new FileReader(args[0])); w = new PrintWriter(System.out); } else { r = new BufferedReader(new FileReader(args[0])); w = new PrintWriter(new FileWriter(args[1])); } long start = System.nanoTime(); doIt(r, w); w.flush(); long stop = System.nanoTime(); System.out.println("Execution time: " + 1e-9 * (stop-start)); } catch (IOException e) { System.err.println(e); System.exit(-1); } } } 

part0 example:

public class Part0 { /** * Read lines one at a time from r. After reading all lines, output * all lines to w, outputting duplicate lines only once. Note: the order * of the output is unspecified and may have nothing to do with the order * that lines appear in r. * @param r the reader to read from * @param w the writer to write to * @throws IOException */ public static void doIt(BufferedReader r, PrintWriter w) throws IOException { List l = new ArrayList<>(); for (String line = r.readLine(); line != null; line = r.readLine()) { l.add(line); } for (String text : l) { w.println(text); } } /** * The driver. Open a BufferedReader and a PrintWriter, either from System.in * and System.out or from filenames specified on the command line, then call doIt. * @param args */ public static void main(String[] args) { try { BufferedReader r; PrintWriter w; if (args.length == 0) { r = new BufferedReader(new InputStreamReader(System.in)); w = new PrintWriter(System.out); } else if (args.length == 1) { r = new BufferedReader(new FileReader(args[0])); w = new PrintWriter(System.out); } else { r = new BufferedReader(new FileReader(args[0])); w = new PrintWriter(new FileWriter(args[1])); } long start = System.nanoTime(); doIt(r, w); w.flush(); long stop = System.nanoTime(); System.out.println("Execution time: " + 1e-9 * (stop-start)); } catch (IOException e) { System.err.println(e); System.exit(-1); } } }