使用 ListIterator 编写插入排序

Question

I am trying to write an insertion sort method that takes in a list of Integers and sorts it in increasing order by using ListIterator. I tried running the method on my main method to see if it has worked but, I end up with a bunch of errors. I would like to know what mistakes I have made and how you would write the code. Here is the method:

public static void insertionsort(LinkedList<Integer> arr){
ListIterator<Integer> it = arr.listIterator();
while(it.hasNext()){
  while(it.hasPrevious()){
    Integer curr = it.next();
    it.previous();
    Integer prev = it.previous();
    if(curr<prev){
      it.set(curr);
      it.next();
      it.next();
      it.set(prev);
    }
  }
  it.next();
}

}

Here is the main method:

public static void main(String[] args){
LinkedList<Integer> a = new LinkedList<Integer>();
a.add(40);
a.add(30);
a.add(20);
a.add(10);
a.add(5);
insertionsort(a);
ListIterator<Integer> i = a.listIterator();
while(i.hasNext()){
  System.out.println(i.next());
}

}

Answer 1

When this condition

curr<prev

is not met you go into an infinite loop because you are leaving the cursor at the same place .

You could do something like this although not very efficient (but still insertion sort), but very easy to understand:

    ListIterator<Integer> iter = arr.listIterator();
    Integer current = iter.next();
    Integer next = null;
    while (iter.hasNext()) {
        if (!iter.hasPrevious() && next != null) {
            //insertion into sorted sublist
            while (iter.hasNext() && iter.next() < next) ;
            iter.previous();
            iter.add(next);
        }
        next = iter.next();
        //nothing to do, keep going
        if (next >= current) {
            current = next;
        } else {
            //remove misplaced element, and check where to put it
            iter.remove();
            //we can go backwards and check or move to the beginning and keep checking
            iter = arr.listIterator();
            current = next;
        }
    }