I don't have much on this... my assignment is to create a recursion method that will output the highest value in an ArrayList of integers.
public static int maxValue(ArrayList<Integer> a)
{
if (a.isEmpty()) throw new NoSuchElementException ("Can't compute max of empty list.");
if(a.size()==1){return a.get(0);}
else {
//not sure what to add here for the recursion
}
}
A way to do this is actually compare the first two values and remove the smallest one ( or one of them if equal) and set a base case of list size 1 like this:
public static int maxValue(ArrayList<Integer> a)
{
if (a.isEmpty()) return -1;
if (a.size() == 1) return a.get(0);
if (a.get(0) <= a.get(1))
{
a.remove(0);
} else
{
a.remove(1);
}
return maxValue(a);
}
Try this:
import java.util.List;
import static java.util.Math.*;
import java.util.NoSuchElementException;
import static java.util.Objects.*;
public static int maxValue( List<Integer> list )
{
if( isNull( list ) ) throw new IllegalArgumentException( "list is null." );
if( list.isEmpty() ) throw new NoSuchElementException( "Can't compute max of empty list." );
var size = list.size();
var head = list.get( 0 );
var retValue = size == 1 ? head : max( head, maxValue( list.sublist( 1, size ) );
return retValue;
}
List.subList() does not return a copy of the (sub)list, but a new view on the underlying list.
If the requirements permit, you could add a second parameter n, and pass the size of ArrayList.
...
System.out.println(maxValue(arrlst, arrlst.size()));
...
public static int maxValue(ArrayList<Integer> a, int n) {
if (n == 1)
return a.get(0);
return Math.max(a.get(n - 1), maxValue(a, n - 1));
}
