Question

java code

level: beginner

write a method

sumList()

public static Integer sumList(ArrayList<Integer> list)

This method calculates the sum of all Integer values in a given ArrayList.

For example, if ArrayList<Integer> list contains {1, 2, 3}, a call to sumList(list) should return 1+2+3, which is 6 as an Integer.

• Return null if the list is empty or null.
• Think about the base case.
  • When should the method terminate/end?
  • Under what condition should your method stop making recursive calls and return your expected value?
• Think about the recursive case.
  • Make recursive calls to the method; make sure to call sumList in the method body.
    • How would the input have to change in the recursive call? What should your parameter argument be?
    • Keep in mind, you do not need to keep the original ArrayList content.
• Again, iterative solution will not be accepted; do NOT use loop to solve this problem.

strToList()

public static ArrayList<Character> strToList(String word)

This method transforms a String into an ArrayList<Character> containing each character of the string in order.

For example, strToWord("word") will return an ArrayList<Character> of four characters: {w,o,r,d} .

strToWord("hello world") will return an

ArrayList<Character>: {h,e,l,l,o, ,w,o,r,l,d}

• Return an empty list if the string is empty.
• Return null if the string is null
• Think about base case.
  • When should the method terminate/end?
  • Under what condition should your method stop making recursive calls and return your expected value?
• Think about the recursive case
  • Make recursive calls to the method; make sure to call to strToList
    • How would the input have to change in the recursive call?
    • Keep in mind, you do not need to keep the original ArrayList content.
  • An iterative solution will not be accepted.

findAverage()

public static double findAverage(ArrayList<Integer> list)

This method returns the average value in the given ArrayList.

For example, if ArrayList<Integer> list is {1, 2, 3, 4}, findAverage(list) will return 2.5.

• Return null if the list is empty or null.
• Think about base case.
  • When should the method terminate/end?
  • Under what condition should your method stop making recursive calls and return your expected value?
  • Think about the recursive case
    • Make recursive calls to the method; make sure to make a function call to findAverage
    • How would the input have to change in the recursive call?
• You do not need to keep the original content of the list.
• An iterative solution will not be accepted; do NOT use a for loop.
• Hint: You should use the idea you used in sumList because finding the average requires calculating the sum.
  • However, you cannot use sumList in this method directly. You are only allowed to make function calls to findAverage itself.
  • You cannot call the method sumList in findAverage
  • What operation do you have to do on the sum to find the average?

Answer 1

import java.util.*;
public class Reccursive {
public static Integer sumList(ArrayList<Integer> list)
{
   if(list.size()==0)
       return null;
   if(list.size()==1)
       return list.get(0);
   return list.remove(0)+sumList(list);
}

public static ArrayList<Character> strToList(String word)
{
ArrayList<Character> clis=new ArrayList<Character>();
if(word.length()==0)
   return null;
if(word.length()==1)
   {clis.add(word.charAt(0));
   return clis;
   }
clis.add(word.charAt(0));
clis.addAll(strToList(word.substring(1)));
return clis;
}

public static Double findAverage(ArrayList<Integer> list)
{

   int n=list.size();
   if(n==0)
       return null;
   if(n==1)
       return 1.0*list.get(0);
   //System.out.println(list);
   return (list.remove(0)+findAverage(list)*(n-1))/(1.0*n);
}

public static void main(String[] args) {
   ArrayList<Integer> list =new ArrayList<Integer>();
   System.out.println("sum of {1,2,3}=");
   list.add(1);list.add(2);list.add(3);
   System.out.println(Reccursive.sumList(list));
   System.out.println("hello world to list:");
   System.out.println(Reccursive.strToList("Hello world"));
   ArrayList<Integer> list2 =new ArrayList<Integer>();
   list2.add(1);list2.add(2);list2.add(3);list2.add(4);
   System.out.println("Average of {1,2,3,4}=");
   System.out.println(Reccursive.findAverage(list2));
  
}
}