在对象作为单链接列表中的参数传递之前删除元素

Question

I'm trying to write a method for to remove an element before the object passed in as a parameter in a Singly Linked List.

So far I have this, but honestly I'm completely lost.

public void removeElementBefore(Object o) {

  Node n = new Node(o);
  Node crt = head;

  // trying to find the element right before the parameter
  while(crt.next != n)
    crt = crt.next;

  // getting the new content
  n = crt.next.content;

  return n;
  }
}

More of the program for context: method to remove last element in the list

public Object removeLast() throws EmptyListException {

    if (head == null) throw new EmptyListException();

    Object o;

    // If there is only one element, we need to modify the head of the list
    if (head.next == null) {
      o = head.content;
      head.content = null;
      head = null;
      return o;
    }

    // We need to go to the second-to-last element
    Node crt = head;
    while (crt.next.next != null)
      crt = crt.next;

    // Now get the content
    o = crt.next.content;

    // Remove all references that are not needed
    crt.next.content = null;
    crt.next = null;

    // And we're done
    return o;
  }

Answer 1

public Object removeElementBefore(Object o) {
    if (o == null)
        return null;

    Node prev = head;
    Node crt = prev == null ? null : prev.next;
    if (crt == null)
        return null;

    // trying to find the element right before the parameter
    while(crt.next != null && !o.equals(crt.next.content)) {
        prev = prev.next;
        crt = crt.next;
    }

    if (crt.next == null)
        return null;

    // remove crt node from list
    prev.next = crt.next;
    crt.next = null;

    // return the removed content
    return crt.content;
}

Answer 2

Here's a non-Java specific algorithm (not necessarily completely compact). You should be able to translate it into Java code.

Given linked list L and item to remove item .

cur = L.head
if (cur == item)
   L.head = cur.next
   return
prev = cur
cur = cur.next
while (cur != item):
    if NOT (cur.next exists):
        // cur is the end of the list, so the item doesn't exist in this list
        return
    prev = cur
    cur = cur.next

// If you reach this point, the desired item has been found, and prev
// precedes it in the list
prev.next = cur.next

Answer 3

public void removeElementBefore(Node before) {
    if (before == null) return;
    Node n = head;

    if (n.next == before) {
        head = n.next;
        return;
    }

    while (n.next.next != before) { 
        if (n.next.next == null) return;
        n = n.next;
    }
    n.next = n.next.next;
}