Solutions to final exam review questions


** Question 1 **************************************************************

//**************************************************
//  Histogram.java         Author: Lewis and Loftus
//
//  Solution to Programming Project 6.4 (page 316).
//**************************************************

import cs1.Keyboard;

public class Histogram {
   public static void main (String[] args) {
      int[] ranges = new int[10];
      int box;

      System.out.println ("Enter some numbers between 0 and 100.");
      System.out.print ("Signal the end by entering ");
      System.out.println ("a number out of that range.");

      int entered = Keyboard.readInt();
      while (entered >= 1 && entered <= 100) {
         box = (entered - 1) / 10;  //note integer division 
         ranges[box] ++;
         entered = Keyboard.readInt();
      }

      // print histogram
      for (box = 0; box < 10; box++) {
         System.out.print((10 * box + 1) + "-");
         System.out.print((10 * box + 10) + "\t|");
         for (int count = 0; count < ranges[box]; count++)
            System.out.print ("*");
         System.out.println ();
      }
   }
}


** Question 2 **************************************************************

// Return 1-d array of "row sums" of ragged, row-major, 2-d array.
// Assume all rows exist.  Input argument is reference to 2-d array: a
public static double[] sum2dArray(double[][] a) {
   double[] sums = new double[a.length];  // 1-d array to store row sums

   for (int r=0; r<a.length; r++) {
      sums[r] = a[r][0];  // sum of row r so far
      for (int c=1; j<a[r].length; c++)
         sums[r] += a[r][c];
   }

   return sums;
}

public static void main(String[] args) {
   // Example method call to sum2dArray (assume in same class)
   double[] rowSums = sum2dArray(new double[][] {{1,2,3},{4,5}});
}


** Question 3 **************************************************************

//Notice that re-ordering rows involves less work than re-ordering columns
//since the matrix is in row-major order.  Parts A and B are put together
//in one class for convenience in testing.  You do not have to do the same.

public class Review3 {

	public static double colsum(double array[][], int j) {
	        int total = 0;
		for (int i = 0; i < array.length; i++)
			total += array[i][j];
		return total;
	}

	public static void select_sort_col(double[][] array){
		int min_loc;  // index of min in unsorted segment
		double temp;

		// loop from first to second last element
	   	   for (int i=0; i<array[0].length-1; i++){

			// find index of min in unsorted segment
			   min_loc = i;
		   	   // compare each element j in unsorted seg with min
      		              for (int j=i+1; j<array[0].length; j++)
			         if (colsum(array,j)<colsum(array,min_loc))
			            min_loc = j;

			// swap ith column with min column
			   for (int k = 0; k < array.length; k++) {
				temp = array[k][min_loc];
	 		   	array[k][min_loc] = array[k][i];
		   	   	array[k][i] = temp;
			   }
		   }
	} //method select_sort_row

	public static double sum(double[] array) {
		int total = 0;
		for (int i = 0; i < array.length; i++)
			total += array[i];
		return total;
	}

	public static void select_sort_row(double[][] array){
		int min_loc;  // index of min in unsorted segment
		double[] temp;

		// loop from first to second last element
	   	   for (int i=0; i<array.length-1; i++){

			// find index of min in unsorted segment
			   min_loc = i;
		   	   // compare each element j in unsorted seg with min
      		              for (int j=i+1; j<array.length; j++)
			         if (sum(array[j])<sum(array[min_loc]))
			            min_loc = j;

			// swap ith element with min
		  	   temp = array[min_loc];
			   array[min_loc] = array[i];
		   	   array[i] = temp;
		   }
	} //method select_sort_row

	public static void main(String[] args) {
	    double[][] x = new double[][]{{45,5,6,4,1,9,4,4},{2,6,3,4,5,5,6,3},
					  {2,3,4,5,6,7,8,9}};
    	
	    for (int i=0; i<x.length; i++) {
		for (int j=0; j<x[i].length; j++)
		  System.out.print(x[i][j] + " ");
		System.out.println();
	    }
    	    System.out.println();

  	    select_sort_col(x);

	    for (int i=0; i<x.length; i++) {
		for (int j=0; j<x[i].length; j++)
		  System.out.print(x[i][j] + " ");
		System.out.println();
	    }
    	    System.out.println();
	} //main
}


** Question 4 **************************************************************

1. Inherited variables:  id
   Inherited methods:  toString (but overridden), clean, report, countRooms
   "Inherited" means "can be accessed as though locally declared"

2. Overload method majorCleanUp:

  // Call method clean x times
  public void majorCleanUp(int x) {
    for (int j=0; j<x; j++)  clean();
  }

3. A few example method calls in client class MyHouse:

  public class MyHouse {
    public static void main(String[] args) {

      Room[] r = new Room[3];

      r[0] = new Room(5);
      r[1] = new Bathroom(10,true);

      r[0].report();  // what is the output?
      r[1].report();  // valid.  what is the output?
      ((Bathroom)r[1]).majorCleanup();  // ok
      ((Bathroom)r[1]).majorCleanup(3);  // also ok

      // Try more examples!
    }
  }


** Question 5 **************************************************************

3
7
15


** Question 6 **************************************************************

//*********************************************************
// Solution 1:  Code segment to count vowels in String str

int[] vfreq = new int[5];  // Array of vowel frequencies
                           // An array is an object, so each cell
                           // is automatically initialized to 0

for (int j=0; j<str.length(); j++) {  //note length METHOD, not CONSTANT

   if (str.charAt(j)=='A' || str.charAt(j)=='a')  vfreq[0]++;
   else if (str.charAt(j)=='E' || str.charAt(j)=='e')  vfreq[1]++;
   else if (str.charAt(j)=='I' || str.charAt(j)=='i')  vfreq[2]++;
   else if (str.charAt(j)=='O' || str.charAt(j)=='o')  vfreq[3]++;
   else if (str.charAt(j)=='U' || str.charAt(j)=='u')  vfreq[4]++;

}


//*********************************************************
// Solution 2:  Code segment to count vowels in String str

int[] vfreq = new int[5];  // Array of vowel frequencies

final String vowelsUp = "AEIOU";
final String vowelsLo = "aeiou";  // vowelsLo = vowelsUp.toLowerCase();

for (int j=0; j<str.length(); j++) {

   for (int v=0; v<vowelsUp.length(); v++)
      if ( str.charAt(j)==vowelsUp.charAt(v) ||
           str.charAt(j)==vowelsLo.charAt(v)    )  vfreq[v]++;

}