forked from exercism/java
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathDeque.java
More file actions
57 lines (47 loc) · 1.24 KB
/
Deque.java
File metadata and controls
57 lines (47 loc) · 1.24 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
public final class Deque<T> {
private Element<T> head;
public void push(T value) {
if (head == null) {
head = new Element<>(value, null, null);
head.next = head;
head.prev = head;
return;
}
Element<T> oldTail = head.prev;
Element<T> tail = new Element<>(value, oldTail, head);
oldTail.next = tail;
head.prev = tail;
}
public T pop() {
head = head.prev;
return shift();
}
public void unshift(T value) {
push(value);
head = head.prev;
}
public T shift() {
T value = head.value;
Element<T> newHead = head.next;
Element<T> newTail = head.prev;
if (newHead == head) {
head = null;
}
else {
newHead.prev = newTail;
newTail.next = newHead;
head = newHead;
}
return value;
}
private static final class Element<T> {
private final T value;
private Element<T> prev;
private Element<T> next;
public Element(T value, Element<T> prev, Element<T> next) {
this.value = value;
this.prev = prev;
this.next = next;
}
}
}