// used for Object, null included
// and here use hashmap rather than hashtable,
// for any null object can not be used as a key or as a value in hashtable.
static void doRemove1(SinglyLinkedList<Character> s) {
HashMap<Character, Boolean> map = new HashMap<Character, Boolean>();
SinglyLinkedList.Node<Character> pre = null;
SinglyLinkedList.Node<Character> node = s.getHead();
while (node != null) {
if (map.containsKey(node.item)) {
pre.next = node.next;
s.decreaseSize();
} else {
map.put(node.item, true);
// 发现新值后再改变pre，不需要把head单独考虑，因为是从后面开始删除
pre = node;
}
// pre = node;
node = node.next;
}
}
// only for Character, assume all ascii, without null
static void doRemove(SinglyLinkedList<Character> s) {
boolean[] check = new boolean[256];
SinglyLinkedList.Node<Character> pre = null;
SinglyLinkedList.Node<Character> node = s.getHead();
while (node != null) {
if (node.item == null) {
System.out.println("---- Warning: null included! remove fail, use function doRemove1()");
return;
}
if (check[node.item]) {
pre.next = node.next;
s.decreaseSize();
} else // else 可以节省运算次数
check[node.item] = true;
pre = node;
node = node.next;
}
}
// use three references, pre, current, runner. No space consume
static void doRemove2(SinglyLinkedList<Character> s) {
SinglyLinkedList.Node<Character> pre = null;
SinglyLinkedList.Node<Character> current = null;
SinglyLinkedList.Node<Character> runner = null;
pre = s.getHead();
current = pre.next;
while (current != null) {
runner = s.getHead();
while (runner != current) {
if (runner.item == current.item) {
pre.next = current.next;
current = current.next;
s.decreaseSize();
break;
}
runner = runner.next;
}
if (runner == current) {
pre = current;
current = current.next;
}
}
}