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// A priority queue data structure.
package container_priority_queue
import "base:builtin"
import "base:runtime"
Priority_Queue :: struct($T: typeid) {
queue: [dynamic]T,
less: proc(a, b: T) -> bool,
swap: proc(q: []T, i, j: int),
}
DEFAULT_CAPACITY :: 16
default_swap_proc :: proc($T: typeid) -> proc(q: []T, i, j: int) {
return proc(q: []T, i, j: int) {
q[i], q[j] = q[j], q[i]
}
}
init :: proc(pq: ^$Q/Priority_Queue($T), less: proc(a, b: T) -> bool, swap: proc(q: []T, i, j: int), capacity := DEFAULT_CAPACITY, allocator := context.allocator) -> (err: runtime.Allocator_Error) {
if pq.queue.allocator.procedure == nil {
pq.queue.allocator = allocator
}
reserve(pq, capacity) or_return
pq.less = less
pq.swap = swap
return .None
}
init_from_dynamic_array :: proc(pq: ^$Q/Priority_Queue($T), queue: [dynamic]T, less: proc(a, b: T) -> bool, swap: proc(q: []T, i, j: int)) {
pq.queue = queue
pq.less = less
pq.swap = swap
n := builtin.len(pq.queue)
for i := n/2 - 1; i >= 0; i -= 1 {
_shift_down(pq, i, n)
}
}
destroy :: proc(pq: ^$Q/Priority_Queue($T)) {
clear(pq)
delete(pq.queue)
}
reserve :: proc(pq: ^$Q/Priority_Queue($T), capacity: int) -> (err: runtime.Allocator_Error) {
return builtin.reserve(&pq.queue, capacity)
}
clear :: proc(pq: ^$Q/Priority_Queue($T)) {
builtin.clear(&pq.queue)
}
len :: proc(pq: $Q/Priority_Queue($T)) -> int {
return builtin.len(pq.queue)
}
cap :: proc(pq: $Q/Priority_Queue($T)) -> int {
return builtin.cap(pq.queue)
}
_shift_down :: proc(pq: ^$Q/Priority_Queue($T), i0, n: int) -> bool {
// O(n log n)
if 0 > i0 || i0 > n {
return false
}
i := i0
queue := pq.queue[:]
for {
j1 := 2*i + 1
if j1 < 0 || j1 >= n {
break
}
j := j1
if j2 := j1+1; j2 < n && pq.less(queue[j2], queue[j1]) {
j = j2
}
if !pq.less(queue[j], queue[i]) {
break
}
pq.swap(queue, i, j)
i = j
}
return i > i0
}
_shift_up :: proc(pq: ^$Q/Priority_Queue($T), j: int) {
j := j
queue := pq.queue[:]
for 0 <= j {
i := (j-1)/2
if i == j || !pq.less(queue[j], queue[i]) {
break
}
pq.swap(queue, i, j)
j = i
}
}
// NOTE(bill): When an element at index 'i' has changed its value, this will fix the
// the heap ordering. This is using a basic "heapsort" with shift up and a shift down parts.
fix :: proc(pq: ^$Q/Priority_Queue($T), i: int) {
if !_shift_down(pq, i, builtin.len(pq.queue)) {
_shift_up(pq, i)
}
}
push :: proc(pq: ^$Q/Priority_Queue($T), value: T) -> (err: runtime.Allocator_Error) {
append(&pq.queue, value) or_return
_shift_up(pq, builtin.len(pq.queue)-1)
return .None
}
pop :: proc(pq: ^$Q/Priority_Queue($T), loc := #caller_location) -> (value: T) {
assert(condition=builtin.len(pq.queue)>0, loc=loc)
n := builtin.len(pq.queue)-1
pq.swap(pq.queue[:], 0, n)
_shift_down(pq, 0, n)
return builtin.pop(&pq.queue)
}
pop_safe :: proc(pq: ^$Q/Priority_Queue($T), loc := #caller_location) -> (value: T, ok: bool) {
if builtin.len(pq.queue) > 0 {
n := builtin.len(pq.queue)-1
pq.swap(pq.queue[:], 0, n)
_shift_down(pq, 0, n)
return builtin.pop_safe(&pq.queue)
}
return
}
remove :: proc(pq: ^$Q/Priority_Queue($T), i: int) -> (value: T, ok: bool) {
n := builtin.len(pq.queue)
if 0 <= i && i < n {
pq.swap(pq.queue[:], i, n-1)
_shift_down(pq, i, n-1)
_shift_up(pq, i)
value, ok = builtin.pop(&pq.queue), true
}
return
}
peek_safe :: proc(pq: $Q/Priority_Queue($T), loc := #caller_location) -> (res: T, ok: bool) {
if builtin.len(pq.queue) > 0 {
return pq.queue[0], true
}
return
}
peek :: proc(pq: $Q/Priority_Queue($T), loc := #caller_location) -> (res: T) {
assert(condition=builtin.len(pq.queue)>0, loc=loc)
if builtin.len(pq.queue) > 0 {
return pq.queue[0]
}
return
}
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