Add pairing heap module
This commit is contained in:
K. Lange
parent
2685f49d24
commit
80754593ad
104
modules/pheap.krk
Normal file
104
modules/pheap.krk
Normal file
@ -0,0 +1,104 @@
|
||||
'''
|
||||
@brief Pairing heap.
|
||||
@author K. Lange <klange@toaruos.org>
|
||||
|
||||
Provides a simple min-heap with insert, pop, peek, and visit.
|
||||
|
||||
A Kuroko implementation is provided as a backup alongside a
|
||||
faster C implementation in a shared object module.
|
||||
'''
|
||||
|
||||
def __make_pheap():
|
||||
def pheap_meld(left, right, comp):
|
||||
if left is None:
|
||||
return right
|
||||
if right is None:
|
||||
return left
|
||||
if comp(left[0],right[0]):
|
||||
if left[1]:
|
||||
right[2] = left[1]
|
||||
left[1] = right
|
||||
return left
|
||||
else:
|
||||
if right[1]:
|
||||
left[2] = right[1]
|
||||
right[1] = left
|
||||
return right
|
||||
|
||||
def pheap_merge_pairs(lst, comp):
|
||||
if lst is None:
|
||||
return None
|
||||
else if lst[2] is None:
|
||||
return lst
|
||||
else:
|
||||
let next = lst[2]
|
||||
lst[2] = None
|
||||
let rest = next[2]
|
||||
next[2] = None
|
||||
return pheap_meld(pheap_meld(lst,next,comp), pheap_merge_pairs(rest, comp), comp)
|
||||
|
||||
def pheap_delete_min(heap, comp):
|
||||
let subs = heap[1]
|
||||
return pheap_merge_pairs(subs, comp)
|
||||
|
||||
def pheap_visit_heap(heap, func):
|
||||
if not heap: return
|
||||
func(heap)
|
||||
pheap_visit_heap(heap[1], func)
|
||||
pheap_visit_heap(heap[2], func)
|
||||
|
||||
def pheap_visit_heap_after(heap, func):
|
||||
if not heap: return
|
||||
pheap_visit_heap(heap[1], func)
|
||||
pheap_visit_heap(heap[2], func)
|
||||
func(heap)
|
||||
|
||||
class PHeap:
|
||||
def __init__(self, comp):
|
||||
'''Create a new pairing heap governed by the given comparator function.'''
|
||||
self.heap = None
|
||||
self.comp = comp
|
||||
self.count = 0
|
||||
|
||||
def insert(self, value):
|
||||
'''Insert a new element into the heap.'''
|
||||
self.heap = pheap_meld(self.heap, [value, None, None], self.comp)
|
||||
self.count += 1
|
||||
|
||||
def peek(self):
|
||||
'''Retrieve the root (smallest) element of the heap, or None if it is empty.'''
|
||||
return self.heap[0] if self.heap else None
|
||||
|
||||
def pop(self):
|
||||
'''Remove and return the root (smallest) element of the heap. If the heap is empty, IndexError is raised.'''
|
||||
let out = self.heap
|
||||
if not out:
|
||||
raise IndexError('pop from empty heap')
|
||||
self.heap = pheap_delete_min(self.heap, self.comp)
|
||||
self.count -= 1
|
||||
return out[0] if out else None
|
||||
|
||||
def __bool__(self):
|
||||
return self.heap is not None
|
||||
|
||||
def __len__(self):
|
||||
return self.count
|
||||
|
||||
def visit(self, func, after=False):
|
||||
'''Call a function for each element of the heap.'''
|
||||
(pheap_visit_heap_after if after else pheap_visit_heap)(self.heap, func)
|
||||
|
||||
# Clean up qualified name.
|
||||
PHeap.__qualname__ = 'PHeap'
|
||||
|
||||
return PHeap
|
||||
|
||||
# Keep the Kuroko version available for testing.
|
||||
let PHeap_krk = __make_pheap()
|
||||
let PHeap = PHeap_krk
|
||||
|
||||
# Try to load the C implementation.
|
||||
try:
|
||||
import _pheap
|
||||
PHeap = _pheap.PHeap
|
||||
|
||||
315
src/modules/module__pheap.c
Normal file
315
src/modules/module__pheap.c
Normal file
@ -0,0 +1,315 @@
|
||||
/**
|
||||
* @brief Pairing heap.
|
||||
* @file module__pheap.c
|
||||
* @author K. Lange <klange@toaruos.org>
|
||||
*
|
||||
* A very simple pairing heap.
|
||||
*
|
||||
* Provides a min-heap with insert, peek, and pop.
|
||||
*
|
||||
* While heap entries may be mutable, care should be taken not to modify
|
||||
* any values used for comparison, as the heap can not update ordering.
|
||||
*
|
||||
* This could likely be improved by the implementation of parent pointers,
|
||||
* which can allow for elements of the heap other than the root to be
|
||||
* removed or updated (removal + reinsertion), but that requires the
|
||||
* ability to quickly reference specific elements - which requires the
|
||||
* heap "nodes" to also be accessible or addressible in some way, such
|
||||
* as by making them Kuroko objects. Such a change would likely result
|
||||
* in performance impacts, so a parent-pointer pairing heap should be
|
||||
* a separate class.
|
||||
*
|
||||
* The implementation here is based strongly on the pseudocode found in
|
||||
* the Wikipedia article "Paring heap".
|
||||
*/
|
||||
#include <assert.h>
|
||||
#include <stdlib.h>
|
||||
#include <kuroko/vm.h>
|
||||
#include <kuroko/util.h>
|
||||
|
||||
static KrkClass * PHeapClass;
|
||||
|
||||
/**
|
||||
* @brief Heap node.
|
||||
*
|
||||
* Represents one element in the heap. Each element potentially has
|
||||
* a pointer to more elements (a "right" or "next" pointer) and a
|
||||
* pointer to a subheap (a "left" pointer).
|
||||
*/
|
||||
typedef struct PHeap PHeap;
|
||||
struct PHeap {
|
||||
struct PHeap_Obj * owner;
|
||||
KrkValue value;
|
||||
PHeap * subheaps; /* Left pointer to first child, if any. */
|
||||
PHeap * next; /* Right pointer to next sibling, if any. */
|
||||
};
|
||||
|
||||
/**
|
||||
* @brief Heap comparator function.
|
||||
*
|
||||
* The heap is ostensibly a min-heap, but the comparison behavior is left
|
||||
* entirely to the user. A comparator function should return true if the
|
||||
* left (first) argument has priority (is less than) the right (second)
|
||||
* argument, and 0 otherwise. This comparison must be consistent or the
|
||||
* heap will not work correctly.
|
||||
*
|
||||
* Generally, this module only uses one comparison function: a wrapper that
|
||||
* calls a Kuroko callable. As Kuroko callables may hold their own state,
|
||||
* no facility was necessary to pass user data to the comparator - only
|
||||
* the left and right heap nodes to compare are given.
|
||||
*/
|
||||
typedef int (*pheap_comparator_func)(PHeap *, PHeap *);
|
||||
|
||||
/**
|
||||
* @brief meld - Combine two heaps.
|
||||
*
|
||||
* Combines two heaps and returns the result. The heaps are "destroyed" in the process.
|
||||
*
|
||||
* @param left One heap. Can be @c NULL for an empty heap.
|
||||
* @param right The other heap. Can be @c NULL for an empty heap.
|
||||
* @param comparator Function that should return true if @p left has priority (is less than) @p right.
|
||||
* @returns A pointer to the new root, which will be either of @p left or @p right.
|
||||
*/
|
||||
static PHeap * pheap_meld(PHeap * left, PHeap * right, pheap_comparator_func comparator) {
|
||||
/*
|
||||
* If either of the heaps is "empty" (represented by NULL),
|
||||
* then simply return the other one.
|
||||
*/
|
||||
if (!left) {
|
||||
return right;
|
||||
}
|
||||
if (!right) {
|
||||
return left;
|
||||
}
|
||||
|
||||
/*
|
||||
* Otherwise, pull the 'smaller' of the two up and add the 'larger'
|
||||
* to the front of the subheap list of the smaller one. We use
|
||||
* intrusive lists within our Heap struct, so each Heap is also
|
||||
* a List node (with a `next` pointer).
|
||||
*/
|
||||
if (comparator(left, right)) {
|
||||
/* Turns `left` into Heap(left→value, right :: left→subheaps) */
|
||||
if (left->subheaps) {
|
||||
right->next = left->subheaps;
|
||||
}
|
||||
left->subheaps = right;
|
||||
return left;
|
||||
} else {
|
||||
/* Turns `right` into Heap(right→value, left :: right→subheaps) */
|
||||
if (right->subheaps) {
|
||||
left->next = right->subheaps;
|
||||
}
|
||||
right->subheaps = left;
|
||||
return right;
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* @brief merge_pairs - Perform left-to-right/right-to-left merge on lists of subheaps.
|
||||
*
|
||||
* The core of the heap.
|
||||
*
|
||||
* @param list List of pairs to merge.
|
||||
* @param comparator Comparator function as described in @c pheap_meld.
|
||||
* @returns the resulting heap.
|
||||
*/
|
||||
static PHeap * pheap_merge_pairs(PHeap * list, pheap_comparator_func comparator) {
|
||||
if (!list) {
|
||||
/* An empty list is represented by NULL, and yields an empty Heap,
|
||||
* which is also represented by NULL... */
|
||||
return NULL;
|
||||
} else if (list->next == NULL) {
|
||||
/* If a list entry doesn't have a next, it has a size of one,
|
||||
* and we can just return this heap directly. */
|
||||
return list;
|
||||
} else {
|
||||
/* Otherwise we meld the first two, then meld them with the result of
|
||||
* recursively melding the rest, which performs our left-right /
|
||||
* right-left two-stage merge. */
|
||||
PHeap * next = list->next;
|
||||
list->next = NULL;
|
||||
PHeap * rest = next->next;
|
||||
next->next = NULL;
|
||||
return pheap_meld(pheap_meld(list, next, comparator), pheap_merge_pairs(rest, comparator), comparator);
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* @brief delete_min - Remove the 'smallest' value from the heap.
|
||||
*
|
||||
* Removes the root node of the heap, rebalancing the remainder
|
||||
* of the heap. Should only be used when the heap is not empty.
|
||||
*
|
||||
* @param heap Heap to remove the root of.
|
||||
* @param comparator Comparator function as described in @c pheap_meld.
|
||||
* @returns the resulting heap.
|
||||
*/
|
||||
static PHeap * pheap_delete_min(PHeap * heap, pheap_comparator_func comparator) {
|
||||
PHeap * subs = heap->subheaps;
|
||||
return pheap_merge_pairs(subs, comparator);
|
||||
}
|
||||
|
||||
/**
|
||||
* @brief visit_heap - Call a user function for every node in the heap.
|
||||
*
|
||||
* The function is called before recursing.
|
||||
*
|
||||
* @param heap Heap to walk.
|
||||
* @param func Function to call.
|
||||
* @param extra User data to pass to the function.
|
||||
*/
|
||||
static void pheap_visit_heap(PHeap * heap, void (*func)(PHeap *, void*), void* extra) {
|
||||
if (!heap) return;
|
||||
func(heap, extra);
|
||||
pheap_visit_heap(heap->subheaps, func, extra);
|
||||
pheap_visit_heap(heap->next, func, extra);
|
||||
}
|
||||
|
||||
/**
|
||||
* @brief visit_heap_after - Call a user function for every node in the heap.
|
||||
*
|
||||
* The function is called after recursing, so this is suitable for freeing the
|
||||
* entirety of a heap.
|
||||
*
|
||||
* @param heap Heap to walk.
|
||||
* @param func Function to call.
|
||||
* @param extra User data to pass to the function.
|
||||
*/
|
||||
static void pheap_visit_heap_after(PHeap * heap, void (*func)(PHeap *, void*), void* extra) {
|
||||
if (!heap) return;
|
||||
pheap_visit_heap_after(heap->subheaps, func, extra);
|
||||
pheap_visit_heap_after(heap->next, func, extra);
|
||||
func(heap, extra);
|
||||
}
|
||||
|
||||
struct PHeap_Obj {
|
||||
KrkInstance inst;
|
||||
KrkValue comparator;
|
||||
PHeap * heap;
|
||||
size_t count;
|
||||
};
|
||||
|
||||
#define IS_PHeap(o) (krk_isInstanceOf(o,PHeapClass))
|
||||
#define AS_PHeap(o) ((struct PHeap_Obj*)AS_OBJECT(o))
|
||||
#define CURRENT_CTYPE struct PHeap_Obj *
|
||||
#define CURRENT_NAME self
|
||||
|
||||
KRK_Method(PHeap,__init__) {
|
||||
KrkValue comparator;
|
||||
if (!krk_parseArgs(".V:PHeap", (const char*[]){"comp"}, &comparator)) return NONE_VAL();
|
||||
self->comparator = comparator;
|
||||
return NONE_VAL();
|
||||
}
|
||||
|
||||
static int run_comparator(PHeap * left, PHeap * right) {
|
||||
assert(left->owner == right->owner);
|
||||
krk_push(left->owner->comparator);
|
||||
krk_push(left->value);
|
||||
krk_push(right->value);
|
||||
KrkValue result = krk_callStack(2);
|
||||
if (!IS_BOOLEAN(result)) return 0;
|
||||
return AS_BOOLEAN(result);
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,insert) {
|
||||
KrkValue value;
|
||||
if (!krk_parseArgs(".V",(const char*[]){"value"}, &value)) return NONE_VAL();
|
||||
struct PHeap * node = calloc(sizeof(struct PHeap), 1);
|
||||
node->owner = self;
|
||||
node->value = value;
|
||||
self->heap = pheap_meld(self->heap, node, run_comparator);
|
||||
self->count += 1;
|
||||
return NONE_VAL();
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,peek) {
|
||||
if (self->heap) return self->heap->value;
|
||||
return NONE_VAL();
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,pop) {
|
||||
PHeap * old = self->heap;
|
||||
if (!old) return krk_runtimeError(vm.exceptions->indexError, "pop from empty heap");
|
||||
self->heap = pheap_delete_min(self->heap, run_comparator);
|
||||
self->count -= 1;
|
||||
KrkValue out = old->value;
|
||||
free(old);
|
||||
return out;
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,__bool__) {
|
||||
return BOOLEAN_VAL(self->heap != NULL);
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,__len__) {
|
||||
return INTEGER_VAL(self->count);
|
||||
}
|
||||
|
||||
static void run_visitor(PHeap * heap, void * visitor) {
|
||||
krk_push(*(KrkValue*)visitor);
|
||||
krk_push(heap->value);
|
||||
krk_callStack(1);
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,visit) {
|
||||
KrkValue func;
|
||||
int after = 0;
|
||||
if (!krk_parseArgs(".V|p",(const char*[]){"func","after"},
|
||||
&func, &after)) return NONE_VAL();
|
||||
|
||||
(after ? pheap_visit_heap_after : pheap_visit_heap)(self->heap, run_visitor, &func);
|
||||
|
||||
return NONE_VAL();
|
||||
}
|
||||
|
||||
static void _scan_one(PHeap * heap, void * unused) {
|
||||
krk_markValue(heap->value);
|
||||
}
|
||||
|
||||
static void _pheap_scan(KrkInstance * _self) {
|
||||
struct PHeap_Obj * self = (void*)_self;
|
||||
krk_markValue(self->comparator);
|
||||
pheap_visit_heap(self->heap, _scan_one, NULL);
|
||||
}
|
||||
|
||||
static void _free_one(PHeap * heap, void * unused) {
|
||||
free(heap);
|
||||
}
|
||||
|
||||
static void _pheap_sweep(KrkInstance * _self) {
|
||||
struct PHeap_Obj * self = (void*)_self;
|
||||
pheap_visit_heap_after(self->heap,_free_one, NULL);
|
||||
}
|
||||
|
||||
KRK_Method(PHeap,comp) {
|
||||
return self->comparator;
|
||||
}
|
||||
|
||||
KRK_Module(_pheap) {
|
||||
KRK_DOC(module, "Pairing heap with simple insert and pop-min operations.");
|
||||
|
||||
KrkClass * PHeap = krk_makeClass(module, &PHeapClass, "PHeap", vm.baseClasses->objectClass);
|
||||
KRK_DOC(PHeap,"Pairing heap with simple insert and pop-min operations.");
|
||||
PHeap->allocSize = sizeof(struct PHeap_Obj);
|
||||
PHeap->_ongcscan = _pheap_scan;
|
||||
PHeap->_ongcsweep = _pheap_sweep;
|
||||
|
||||
KRK_DOC(BIND_METHOD(PHeap,__init__),
|
||||
"@arguments comp\n\n"
|
||||
"Create a new pairing heap governed by the given comparator function.");
|
||||
KRK_DOC(BIND_METHOD(PHeap,insert),
|
||||
"@arguments value\n\n"
|
||||
"Insert a new element into the heap.");
|
||||
KRK_DOC(BIND_METHOD(PHeap,peek),
|
||||
"Retrieve the root (smallest) element of the heap, or None if it is empty.");
|
||||
KRK_DOC(BIND_METHOD(PHeap,pop),
|
||||
"Remove and return the root (smallest) element of the heap. If the heap is empty, IndexError is raised.");
|
||||
BIND_METHOD(PHeap,__bool__);
|
||||
BIND_METHOD(PHeap,__len__);
|
||||
KRK_DOC(BIND_METHOD(PHeap,visit),
|
||||
"@arguments func,after=False\n\n"
|
||||
"Call a function for each element of the heap.");
|
||||
BIND_PROP(PHeap,comp);
|
||||
krk_finalizeClass(PHeapClass);
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user