forked from timtadh/data-structures
/
pq.go
164 lines (144 loc) · 3.02 KB
/
pq.go
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
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
package heap
import (
"github.com/timtadh/data-structures/errors"
"github.com/timtadh/data-structures/types"
)
type entry struct {
item interface{}
priority int
}
type PriorityQueue interface {
types.Sized
Push(priority int, item interface{})
Peek() interface{}
Pop() interface{}
}
// Notes:
// Parent of i : (i+1)/2 - 1
// Left Child of i : (i+1)*2 - 1
// Right Child of i : (i+1)*2
// A binary heap for Priority Queues. The priorities are modeled
// explicitly as integers. It can work either as a min heap or a max
// heap.
type Heap struct {
min bool
list []entry
}
// Make a new binary heap.
// size : hint for the size of the heap
// (should estimate the maximal size)
// min : false == max heap, true == min heap
func NewHeap(size int, min bool) *Heap {
return &Heap{
min: min,
list: make([]entry, 0, size),
}
}
func NewMinHeap(size int) *Heap {
return &Heap{
min: true,
list: make([]entry, 0, size),
}
}
func NewMaxHeap(size int) *Heap {
return &Heap{
min: false,
list: make([]entry, 0, size),
}
}
// How many items in the heap?
func (h *Heap) Size() int {
return len(h.list)
}
// Is this a min heap?
func (h *Heap) MinHeap() bool {
return h.min
}
// Is this a max heap?
func (h *Heap) MaxHeap() bool {
return !h.min
}
// Push an item with a priority
func (h *Heap) Push(priority int, item interface{}) {
h.list = append(h.list, entry{item, priority})
h.fixUp(len(h.list) - 1)
}
// Pop the highest (or lowest) priority item
func (h *Heap) Pop() interface{} {
if len(h.list) == 0 {
return nil
}
i := h.list[0].item
h.list[0] = h.list[len(h.list)-1]
h.list = h.list[:len(h.list)-1]
h.fixDown(0)
return i
}
// Peek at the highest (or lowest) priority item
func (h *Heap) Peek() interface{} {
if len(h.list) == 0 {
return nil
}
return h.list[0].item
}
func (h *Heap) Items() (it types.Iterator) {
i := 0
return func() (item interface{}, next types.Iterator) {
var e entry
if i < len(h.list) {
e = h.list[i]
i++
return e.item, it
}
return nil, nil
}
}
func (h *Heap) fixUp(k int) {
parent := (k+1)/2 - 1
for k > 0 {
if h.gte(parent, k) {
return
}
h.list[parent], h.list[k] = h.list[k], h.list[parent]
k = parent
parent = (k+1)/2 - 1
}
}
func (h *Heap) fixDown(k int) {
kid := (k+1)*2 - 1
for kid < len(h.list) {
if kid+1 < len(h.list) && h.lt(kid, kid+1) {
kid++
}
if h.gte(k, kid) {
break
}
h.list[kid], h.list[k] = h.list[k], h.list[kid]
k = kid
kid = (k+1)*2 - 1
}
}
func (h *Heap) gte(i, j int) bool {
if h.min {
return h.list[i].priority <= h.list[j].priority
} else {
return h.list[i].priority >= h.list[j].priority
}
}
func (h *Heap) lt(i, j int) bool {
if h.min {
return h.list[i].priority > h.list[j].priority
} else {
return h.list[i].priority < h.list[j].priority
}
}
// Verify the heap is properly structured.
func (h *Heap) Verify() error {
for i := 1; i < len(h.list); i++ {
parent := (i+1)/2 - 1
if h.lt(parent, i) {
return errors.Errorf("parent %v '<' kid %v", h.list[parent], h.list[i])
}
}
return nil
}