1 /*
2 * This file is part of the MicroPython project, http://micropython.org/
3 *
4 * The MIT License (MIT)
5 *
6 * Copyright (c) 2020 Damien P. George
7 *
8 * Permission is hereby granted, free of charge, to any person obtaining a copy
9 * of this software and associated documentation files (the "Software"), to deal
10 * in the Software without restriction, including without limitation the rights
11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
12 * copies of the Software, and to permit persons to whom the Software is
13 * furnished to do so, subject to the following conditions:
14 *
15 * The above copyright notice and this permission notice shall be included in
16 * all copies or substantial portions of the Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
24 * THE SOFTWARE.
25 */
26 #ifndef MICROPY_INCLUDED_PY_PAIRHEAP_H
27 #define MICROPY_INCLUDED_PY_PAIRHEAP_H
28
29 // This is an implementation of a pairing heap. It is stable and has deletion
30 // support. Only the less-than operation needs to be defined on elements.
31 //
32 // See original paper for details:
33 // Michael L. Fredman, Robert Sedjewick, Daniel D. Sleator, and Robert E. Tarjan.
34 // The Pairing Heap: A New Form of Self-Adjusting Heap.
35 // Algorithmica 1:111-129, 1986.
36 // https://www.cs.cmu.edu/~sleator/papers/pairing-heaps.pdf
37
38 #include <assert.h>
39 #include "py/obj.h"
40
41 // This struct forms the nodes of the heap and is intended to be extended, by
42 // placing it first in another struct, to include additional information for the
43 // element stored in the heap. It includes "base" so it can be a MicroPython
44 // object allocated on the heap and the GC can automatically trace all nodes by
45 // following the tree structure.
46 typedef struct _mp_pairheap_t {
47 mp_obj_base_t base;
48 struct _mp_pairheap_t *child;
49 struct _mp_pairheap_t *child_last;
50 struct _mp_pairheap_t *next;
51 } mp_pairheap_t;
52
53 // This is the function for the less-than operation on nodes/elements.
54 typedef int (*mp_pairheap_lt_t)(mp_pairheap_t *, mp_pairheap_t *);
55
56 // Core functions.
57 mp_pairheap_t *mp_pairheap_meld(mp_pairheap_lt_t lt, mp_pairheap_t *heap1, mp_pairheap_t *heap2);
58 mp_pairheap_t *mp_pairheap_pairing(mp_pairheap_lt_t lt, mp_pairheap_t *child);
59 mp_pairheap_t *mp_pairheap_delete(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node);
60
61 // Create a new heap.
mp_pairheap_new(mp_pairheap_lt_t lt)62 static inline mp_pairheap_t *mp_pairheap_new(mp_pairheap_lt_t lt) {
63 (void)lt;
64 return NULL;
65 }
66
67 // Initialise a single pairing-heap node so it is ready to push on to a heap.
mp_pairheap_init_node(mp_pairheap_lt_t lt,mp_pairheap_t * node)68 static inline void mp_pairheap_init_node(mp_pairheap_lt_t lt, mp_pairheap_t *node) {
69 (void)lt;
70 node->child = NULL;
71 node->next = NULL;
72 }
73
74 // Test if the heap is empty.
mp_pairheap_is_empty(mp_pairheap_lt_t lt,mp_pairheap_t * heap)75 static inline bool mp_pairheap_is_empty(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
76 (void)lt;
77 return heap == NULL;
78 }
79
80 // Peek at the top of the heap. Will return NULL if empty.
mp_pairheap_peek(mp_pairheap_lt_t lt,mp_pairheap_t * heap)81 static inline mp_pairheap_t *mp_pairheap_peek(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
82 (void)lt;
83 return heap;
84 }
85
86 // Push new node onto existing heap. Returns the new heap.
mp_pairheap_push(mp_pairheap_lt_t lt,mp_pairheap_t * heap,mp_pairheap_t * node)87 static inline mp_pairheap_t *mp_pairheap_push(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node) {
88 assert(node->child == NULL && node->next == NULL);
89 return mp_pairheap_meld(lt, node, heap); // node is first to be stable
90 }
91
92 // Pop the top off the heap, which must not be empty. Returns the new heap.
mp_pairheap_pop(mp_pairheap_lt_t lt,mp_pairheap_t * heap)93 static inline mp_pairheap_t *mp_pairheap_pop(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
94 assert(heap->next == NULL);
95 mp_pairheap_t *child = heap->child;
96 heap->child = NULL;
97 return mp_pairheap_pairing(lt, child);
98 }
99
100 #endif // MICROPY_INCLUDED_PY_PAIRHEAP_H
101