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public class Sort extends DoublyLinkedList
{
    public static  DoublyLinkedList mergeSort(DoublyLinkedList arr)
    {
        DoublyLinkedList DLL_arr1= new DoublyLinkedList();
        DoublyLinkedList DLL_arr2= new DoublyLinkedList();
        int N = arr.size();
        int k = arr.size()/2;
        
        if(N>2)
        {
            for(int i = 0 ; i<k ;i++)
            {
                DLL_arr1.addLast(arr.removeFirst());
            }
            for(int i = 0 ; i<N-k ;i++)
            {
                DLL_arr2.addLast(arr.removeFirst());
            }
 
            DLL_arr1=mergeSort(DLL_arr1); //DLL_arr1.head=mergeSort(DLL_arr1).head;
            DLL_arr2=mergeSort(DLL_arr2); //DLL_arr2.head=mergeSort(DLL_arr2).head;
        }
        else
        {
            for(int i = 0 ; i<k ;i++)
            {
                DLL_arr1.addLast(arr.removeFirst());
            }
            for(int i = 0 ; i<N-k ;i++)
            {
                DLL_arr2.addLast(arr.removeFirst());
            }
        }
        return merge(DLL_arr1,DLL_arr2);
    }
    private static  DoublyLinkedList merge(DoublyLinkedList DLL_arr1,DoublyLinkedList DLL_arr2)
    {
        DoublyLinkedList returnList= new DoublyLinkedList();
        while((DLL_arr1.size()>0)&&(DLL_arr2.size()>0))
        {
            if(DLL_arr1.head.data<DLL_arr2.head.data)
            {
                returnList.addLast(DLL_arr1.removeFirst());
            }
            else
            {
                returnList.addLast(DLL_arr2.removeFirst());
            }
        }
        if(DLL_arr1.size()>0)
        {
            while(DLL_arr1.size()!=0)
            {
                returnList.addLast(DLL_arr1.removeFirst());
            }
        }
        else if(DLL_arr2.size()>0)
        {
            while(DLL_arr2.size()!=0)
            {
                returnList.addLast(DLL_arr2.removeFirst());
            }
        }
        //System.out.println(returnList.head.data);
        //System.out.println(returnList.head.next.data);
        return returnList;
    }
 
    public static void main(String[] args) {
        Sort S= new Sort();
        DoublyLinkedList DLL= new DoublyLinkedList();
        DLL.addLast(6);
        DLL.addLast(10);
        DLL.addLast(7);
        DLL.addLast(5);
        DLL.addLast(20);
        DLL.addLast(8);
        DLL=mergeSort(DLL);
        while(DLL.size()!=0)
        System.out.println(DLL.removeFirst());   
    }
}
cs


이중 연결리스트로 병합 정렬 구현중인데 mergeSort 부분에서 다시 mergeSort 호출하는 부분에서 처음 짯을때 head값으로 넘겨받으려고 했는데 저렇게 하니까 동작은하는데 병합 정렬을 못해버려서 한참 해맷습니다! 이거 해결할려고 3시간 걸렸는데 왜 head값으로 넘겨주면 작동을 안하는건가요?