import java.util.Arrays; /** * This is a skeleton file for your homework. Edit t
ID: 3783000 • Letter: I
Question
import java.util.Arrays;
/**
* This is a skeleton file for your homework. Edit the sections marked TODO. You
* may add new functions. You may also edit the function "main" to test your
* code.
*
* You must not add static variables. You MAY add static functions, just not
* static variables.
*
* It is okay to add functions, such as
*
* <pre>
* public static double sumHelper (double[] list, int i, double sumSoFar) {
* </pre>
*
* but it is NOT okay to add static variables, such as
*
* <pre>
* public static int x;
* </pre>
*
* As for homework 1, you must not change the declaration of any method.
*
* You can edit the main function all you want. I will not run your main
* function when grading.
*/
public class Recursion {
/**
* As a model, here is a minValue function, both iteratively and recursively
*/
/** iterative version */
public static double minValueIterative (double[] list) {
double result = list[0];
int i = 1;
while (i < list.length) {
if (list[i] < result) result = list[i];
i = i + 1;
}
return result;
}
/** recursive version */
public static double minValue (double[] list) {
return minValueHelper (list, 1, list[0]);
}
private static double minValueHelper (double[] list, int i, double result) {
if (i < list.length) {
if (list[i] < result) result = list[i];
result = minValueHelper (list, i + 1, result);
}
return result;
}
/**
* PROBLEM 1: Translate the following sum function from iterative to
* recursive.
*
* You should write a helper method. You may not use any "fields" to solve
* this problem (a field is a variable that is declared "outside" of the
* function declaration --- either before or after).
*/
public static double sumIterative (double[] a) {
double result = 0.0;
int i = 0;
while (i < a.length) {
result = result + a[i];
i = i + 1;
}
return result;
}
public static double sum (double[] a) {
return 0; // TODO
}
/**
* PROBLEM 2: Do the same translation for this in-place reverse function
*
* You should write a helper method. You may not use any "fields" to solve
* this problem (a field is a variable that is declared "outside" of the
* function declaration --- either before or after).
*/
public static void reverseIterative (double[] a) {
int hi = a.length - 1;
int lo = 0;
while (lo < hi) {
double loVal = a[lo];
double hiVal = a[hi];
a[hi] = loVal;
a[lo] = hiVal;
lo = lo + 1;
hi = hi - 1;
}
}
public static void reverse (double[] a) {
// TODO
}
/**
* @param args
*/
public static void main (String[] args) {
double[] list0 = new double[] {};
double[] list1 = new double[] { 5 };
double[] list2 = new double[] { -3, 5 };
double[] list3 = new double[] { 2, -3, 5 };
double[] list4 = new double[] { -1, 2, -3, 5 };
double[] list5 = new double[] { 33, 44, 55 };
System.out.println("Display the sum of the array contents");
System.out.println ("list5: " +sum (list5));
System.out.println ("list0: " +sum (list0));
System.out.println ("list1: " +sum (list1));
System.out.println ("list2: " +sum (list2));
System.out.println ("list3: " +sum (list3));
System.out.println ("list4: " +sum (list4));
System.out.println("Reversing the lists");
reverse (list0);
System.out.println ("list0: " +Arrays.toString (list0));
reverse (list1);
System.out.println ("list1: " +Arrays.toString (list1));
reverse (list2);
System.out.println ("list2: " +Arrays.toString (list2));
reverse (list3);
System.out.println ("list3: " +Arrays.toString (list3));
reverse (list4);
System.out.println ("list4: " +Arrays.toString (list4));
reverse (list5);
System.out.println ("list5: " +Arrays.toString (list5));
}
}
Explanation / Answer
import java.util.Arrays;
/**
* This is a skeleton file for your homework. Edit the sections marked TODO. You
* may add new functions. You may also edit the function "main" to test your
* code.
*
* You must not add static variables. You MAY add static functions, just not
* static variables.
*
* It is okay to add functions, such as
*
* <pre>
* public static double sumHelper (double[] list, int i, double sumSoFar) {
* </pre>
*
* but it is NOT okay to add static variables, such as
*
* <pre>
* public static int x;
* </pre>
*
* As for homework 1, you must not change the declaration of any method.
*
* You can edit the main function all you want. I will not run your main
* function when grading.
*/
public class Recursion {
/**
* As a model, here is a minValue function, both iteratively and recursively
*/
/** iterative version */
public static double minValueIterative (double[] list) {
double result = list[0];
int i = 1;
while (i < list.length) {
if (list[i] < result) result = list[i];
i = i + 1;
}
return result;
}
/** recursive version */
public static double minValue (double[] list) {
return minValueHelper (list, 1, list[0]);
}
private static double minValueHelper (double[] list, int i, double result) {
if (i < list.length) {
if (list[i] < result) result = list[i];
result = minValueHelper (list, i + 1, result);
}
return result;
}
/**
* PROBLEM 1: Translate the following sum function from iterative to
* recursive.
*
* You should write a helper method. You may not use any "fields" to solve
* this problem (a field is a variable that is declared "outside" of the
* function declaration --- either before or after).
*/
public static double sumIterative (double[] a) {
double result = 0.0;
int i = 0;
while (i < a.length) {
result = result + a[i];
i = i + 1;
}
return result;
}
public static double sum (double[] a) {
if (a.length <= 0) return 0.0;
return sumHelper(a, 1, a[0]);
}
private static double sumHelper (double[] list, int i, double result) {
if (i < list.length) {
result += list[i];
result = sumHelper (list, i + 1, result);
}
return result;
}
/**
* PROBLEM 2: Do the same translation for this in-place reverse function
*
* You should write a helper method. You may not use any "fields" to solve
* this problem (a field is a variable that is declared "outside" of the
* function declaration --- either before or after).
*/
public static void reverseIterative (double[] a) {
int hi = a.length - 1;
int lo = 0;
while (lo < hi) {
double loVal = a[lo];
double hiVal = a[hi];
a[hi] = loVal;
a[lo] = hiVal;
lo = lo + 1;
hi = hi - 1;
}
}
public static void reverse (double[] a) {
if (a.length <= 0) return ;
reverseHelper(a, 0, a.length-1);
}
private static void reverseHelper (double[] list, int lo, int hi) {
if (lo < hi) {
double loVal = list[lo];
double hiVal = list[hi];
list[hi] = loVal;
list[lo] = hiVal;
lo++;
hi--;
reverseHelper(list, lo, hi);
}
}
/**
* @param args
*/
public static void main (String[] args) {
double[] list0 = new double[] {};
double[] list1 = new double[] { 5 };
double[] list2 = new double[] { -3, 5 };
double[] list3 = new double[] { 2, -3, 5 };
double[] list4 = new double[] { -1, 2, -3, 5 };
double[] list5 = new double[] { 33, 44, 55 };
System.out.println("Display the sum of the array contents");
System.out.println ("list5: " +sum (list5));
System.out.println ("list0: " +sum (list0));
System.out.println ("list1: " +sum (list1));
System.out.println ("list2: " +sum (list2));
System.out.println ("list3: " +sum (list3));
System.out.println ("list4: " +sum (list4));
System.out.println("Reversing the lists");
reverse (list0);
System.out.println ("list0: " + Arrays.toString (list0));
reverse (list1);
System.out.println ("list1: " +Arrays.toString (list1));
reverse (list2);
System.out.println ("list2: " +Arrays.toString (list2));
reverse (list3);
System.out.println ("list3: " +Arrays.toString (list3));
reverse (list4);
System.out.println ("list4: " +Arrays.toString (list4));
reverse (list5);
System.out.println ("list5: " +Arrays.toString (list5));
}
}
/*
Sample output
Display the sum of the array contents
list5: 132.0
list0: 0.0
list1: 5.0
list2: 2.0
list3: 4.0
list4: 3.0
Reversing the lists
list0: []
list1: [5.0]
list2: [5.0, -3.0]
list3: [5.0, -3.0, 2.0]
list4: [5.0, -3.0, 2.0, -1.0]
list5: [55.0, 44.0, 33.0]
*/
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