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.
46typedef 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.
54typedef int (*mp_pairheap_lt_t)(mp_pairheap_t *, mp_pairheap_t *);
55
56// Core functions.
57mp_pairheap_t *mp_pairheap_meld(mp_pairheap_lt_t lt, mp_pairheap_t *heap1, mp_pairheap_t *heap2);
58mp_pairheap_t *mp_pairheap_pairing(mp_pairheap_lt_t lt, mp_pairheap_t *child);
59mp_pairheap_t *mp_pairheap_delete(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node);
60
61// Create a new heap.
62static 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.
68static 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.
75static 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.
81static 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.
87static 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.
93static 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