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       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.
      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.
      68                 :        556 : static inline void mp_pairheap_init_node(mp_pairheap_lt_t lt, mp_pairheap_t *node) {
      69                 :        556 :     (void)lt;
      70                 :        556 :     node->child = NULL;
      71         [ +  - ]:        556 :     node->next = NULL;
      72                 :            : }
      73                 :            : 
      74                 :            : // Test if the heap is empty.
      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.
      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.
      87                 :     303293 : static inline mp_pairheap_t *mp_pairheap_push(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node) {
      88   [ +  -  -  + ]:     303293 :     assert(node->child == NULL && node->next == NULL);
      89                 :     303293 :     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.
      93                 :     303173 : static inline mp_pairheap_t *mp_pairheap_pop(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
      94         [ -  + ]:     303173 :     assert(heap->next == NULL);
      95                 :     303173 :     mp_pairheap_t *child = heap->child;
      96                 :     303173 :     heap->child = NULL;
      97                 :     303173 :     return mp_pairheap_pairing(lt, child);
      98                 :            : }
      99                 :            : 
     100                 :            : #endif // MICROPY_INCLUDED_PY_PAIRHEAP_H