Question

I’m having a very hard time using a pseudo code for the shuffling algorithm and turning it to a working java code. I’m attempting to shuffle a linked list. Overall the method takes the pointer of the head of the linked list and returns a pointer to the head of the same list randomly. I want to use a getLength and getItem method I’ve created.

public static ListElement shuffle(ListElement head){
  head = head.getLength();
  ListElement head2= null;
  while( head == null) {
    int random = (int) Math.random() *  n;
    for(int i=0;i<random;i++){
        head= head.getNext();
    }
  }
  return head;    
}

Pseudo code:

A list L of length n
A new list R, empty
while L is not empty
   pick a random k 
   such that 0<=k<= (length L)
   remove the kth element of L
      call it e
   prepend e to R

Answer 1

I just rewrite the code a bit so that it follows the pseudo code.

ListElement head2 = null;
int length = head.getLength();

while (head != null) {
    int k = (int) Math.random() * length;

    // Assume there is function deleteAt(index) that removes
    // the element at specified index and returns the deleted
    // element
    ListElement e = head.deleteAt(k);
    // Although I can just give the implementation - I'll leave this
    // as exercise.

    // You can have a function that add element to front
    // head2.addFront(e);
    e.setNext(head2);
    head2 = e;

    // Instead of querying the length again
    // decrement the length
    length--;
}
return head;