CareerCup

Only considere cases when m >= 1 and n >= 1

public ListNode RemoveRetain(ListNode head, int m, int n)
{
    if (head == null)
        return head;
    if (m == 0 && n == 0)
        return head;
    // If don't skip elements and delete N is an empty list
    if (m == 0)
        return null;
    // If skyp M and don't delete elements is the list is not modified
    if (n == 0)
        return head;

    var fakeHead = new ListNode();
    fakeHead.Next = head;

    var current = fakeHead;
    int count;
    while (current != null)
    {
        count = 0;
        while (current != null && count < m)
        {
            current = current.Next;
            count++;
        }

        if (current == null)
            break;

        var last = current;
        count = 0;
        while (current != null && count < n)
        {
            current = current.Next;
            count++;
        }

        last.Next = (current != null) ? current.Next : null;
    }

    return fakeHead.Next;
}

Not Much different from last

void smartModify(list *head, int m, int n){
	if (head == NULL) return;
	list *cur = head;	
	while (cur != NULL){
		list *mnode = NULL;
		list *nnode = NULL;
		int mnum = m;
		int nnum = n;
		while (cur != NULL && mnum > 0){
			if (--mnum == 0) mnode = cur;
			cur = cur->next;
		}
		while (cur != NULL && nnum > 0){
			if (--nnum == 0) nnode = cur;
			cur = cur->next;
		}
		if (mnode)
			mnode->next = (nnode == NULL) ? NULL : nnode->next;
	}
}

hantsu - Thanks for the program. Works and all edge cases covered!!

@praveen, It will go into infinite loop if m==0 and n==0.