FilesExpand file tree

 master

/

PriorityQueues.java

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

126 lines (115 loc) · 3.05 KB

 master

/

PriorityQueues.java

Copy path

Top

File metadata and controls

• Code
• Blame

126 lines (115 loc) · 3.05 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

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

115

116

117

118

119

120

121

122

123

124

125

126

package DataStructures.Queues;

/**

* This class implements a PriorityQueue.

* <p>

* A priority queue adds elements into positions based on their priority.

* So the most important elements are placed at the front/on the top.

* In this example I give numbers that are bigger, a higher priority.

* Queues in theory have no fixed size but when using an array

* implementation it does.

*/

class PriorityQueue {

/**

* The max size of the queue

*/

private int maxSize;

/**

* The array for the queue

*/

private int[] queueArray;

/**

* How many items are in the queue

*/

private int nItems;

/**

* Constructor

*

* @param size Size of the queue

*/

public PriorityQueue(int size) {

maxSize = size;

queueArray = new int[size];

nItems = 0;

}

/**

* Inserts an element in it's appropriate place

*

* @param value Value to be inserted

*/

public void insert(int value) {

if (isFull()) {

throw new RuntimeException("Queue is full");

} else {

int j = nItems - 1; // index of last element

while (j >= 0 && queueArray[j] > value) {

queueArray[j + 1] = queueArray[j]; // Shifts every element up to make room for insertion

j--;

}

queueArray[j + 1] = value; // Once the correct position is found the value is inserted

nItems++;

}

}

/**

* Remove the element from the front of the queue

*

* @return The element removed

*/

public int remove() {

return queueArray[--nItems];

}

/**

* Checks what's at the front of the queue

*

* @return element at the front of the queue

*/

public int peek() {

return queueArray[nItems - 1];

}

/**

* Returns true if the queue is empty

*

* @return true if the queue is empty

*/

public boolean isEmpty() {

return (nItems == 0);

}

/**

* Returns true if the queue is full

*

* @return true if the queue is full

*/

public boolean isFull() {

return (nItems == maxSize);

}

/**

* Returns the number of elements in the queue

*

* @return number of elements in the queue

*/

public int getSize() {

return nItems;

}

}

/**

* This class implements the PriorityQueue class above.

*

* @author Unknown

*/

public class PriorityQueues {

/**

* Main method

*

* @param args Command Line Arguments

*/

public static void main(String[] args) {

PriorityQueue myQueue = new PriorityQueue(4);

myQueue.insert(10);

myQueue.insert(2);

myQueue.insert(5);

myQueue.insert(3);

// [2, 3, 5, 10] Here higher numbers have higher priority, so they are on the top

for (int i = 3; i >= 0; i--)

System.out.print(myQueue.remove() + " "); // will print the queue in reverse order [10, 5, 3, 2]

// As you can see, a Priority Queue can be used as a sorting algotithm

}

}