-
Notifications
You must be signed in to change notification settings - Fork 0
/
RandomizedQueue.java
114 lines (93 loc) · 2.84 KB
/
RandomizedQueue.java
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
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
import edu.princeton.cs.algs4.StdRandom;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class RandomizedQueue<Item> implements Iterable<Item> {
private Item[] items;
private int size;
// construct an empty randomized queue
public RandomizedQueue() {
items = (Item[]) new Object[1];
size = 0;
}
// is the randomized queue empty?
public boolean isEmpty() {
return size == 0;
}
// return the number of items on the randomized queue
public int size() {
return size;
}
// add the item
public void enqueue(Item item) {
if (item == null) {
throw new IllegalArgumentException();
}
if (items.length == size) {
resize(size * 2);
}
items[size] = item;
size++;
}
// remove and return a random item
public Item dequeue() {
if (size == 0) {
throw new NoSuchElementException();
}
int randomIndex = StdRandom.uniformInt(size);
Item result = items[randomIndex];
items[randomIndex] = items[size - 1];
size--;
if (size > 0 && size == items.length / 4) {
resize(items.length / 2);
}
return result;
}
// return a random item (but do not remove it)
public Item sample() {
if (size == 0) {
throw new NoSuchElementException();
}
int randomIndex = StdRandom.uniformInt(size);
return items[randomIndex];
}
// return an independent iterator over items in random order
public Iterator<Item> iterator() {
return new RandomizedQueueIterator();
}
private void resize(int size) {
Item[] newItems = (Item[]) new Object[size];
for (int i = 0; i < this.size; ++i) {
newItems[i] = items[i];
}
items = newItems;
}
private class RandomizedQueueIterator implements Iterator<Item> {
private Item[] randomItems = (Item[]) new Object[size];
private int len = size;
public RandomizedQueueIterator() {
for (int i = 0; i < randomItems.length; i++) {
randomItems[i] = items[i];
}
}
public boolean hasNext() {
return len != 0;
}
public Item next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
int randomIndex = StdRandom.uniformInt(len);
Item item = randomItems[randomIndex];
randomItems[randomIndex] = randomItems[len - 1];
randomItems[len - 1] = null;
len--;
return item;
}
public void remove() {
throw new UnsupportedOperationException();
}
}
// unit testing (required)
public static void main(String[] args) {
}
}