// CSE 143, Winter 2009, Marty Stepp
//
// This program demonstrates the use of stacks and queues.
// It reads in a file of students' exam scores in reverse order, such as:
//
// Yeilding      Janet      87
// White         Steven     84
// Todd          Kim        52
// 
// And first strips the ones who got 100 on the exam using a queue,
// then prints the rest in reverse order using a stack.

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

public class GradeExams {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner input = new Scanner(new File("exams.txt"));
        Queue<String> students = readStudents(input);
        System.out.println(students);
        
        remove100s(students);
        System.out.println(students);
        
        printReversed(students);
        System.out.println(students);
    }
    
    // Reads the given file into a queue and returns it.
    public static Queue<String> readStudents(Scanner input) {
        Queue<String> students = new LinkedList<String>();
        while (input.hasNextLine()) {
            String line = input.nextLine();
            students.add(line);
        }
        return students;
    }
    
    // I have the students in a queue; now remove students with score of 100
    public static void remove100s(Queue<String> students) {
        int size = students.size();
        for (int i = 0; i < size; i++) {
            String student = students.remove();   // "Todd   Kim   52"
            if (!student.endsWith("100")) {
                students.add(student);
            }
        }
    }
    
    // Prints the contents of the given queue in reverse order.
    // Postcondition: The queue is unmodified from its original state when the method returns.
    public static void printReversed(Queue<String> students) {
        Queue<String> backup = new LinkedList<String>();
        Stack<String> s = new Stack<String>();
        
        // load all students into a stack (for printing) and backup queue (for restoring)
        while (!students.isEmpty()) {
            String line = students.remove();
            backup.add(line);
            s.push(line);
        }
        
        // print the elements of the queue in reverse order (using the stack)
        while (!s.isEmpty()) {
            System.out.println(s.pop());
        }
        
        // restore the queue to its original state
        while (!backup.isEmpty()) {
            students.add(backup.remove());
        }
        
    }
}