NAME
Image::Leptonica::Func::heap
VERSION
version 0.04
heap.c
heap.c
Create/Destroy L_Heap
L_HEAP *lheapCreate()
void *lheapDestroy()
Operations to add/remove to/from the heap
l_int32 lheapAdd()
static l_int32 lheapExtendArray()
void *lheapRemove()
Heap operations
l_int32 lheapSwapUp()
l_int32 lheapSwapDown()
l_int32 lheapSort()
l_int32 lheapSortStrictOrder()
Accessors
l_int32 lheapGetCount()
Debug output
l_int32 lheapPrint()
The L_Heap is useful to implement a priority queue, that is sorted
on a key in each element of the heap. The heap is an array
of nearly arbitrary structs, with a l_float32 the first field.
This field is the key on which the heap is sorted.
Internally, we keep track of the heap size, n. The item at the
root of the heap is at the head of the array. Items are removed
from the head of the array and added to the end of the array.
When an item is removed from the head, the item at the end
of the array is moved to the head. When items are either
added or removed, it is usually necesary to swap array items
to restore the heap order. It is guaranteed that the number
of swaps does not exceed log(n).
-------------------------- N.B. ------------------------------
The items on the heap (or, equivalently, in the array) are cast
to void*. Their key is a l_float32, and it is REQUIRED that the
key be the first field in the struct. That allows us to get the
key by simply dereferencing the struct. Alternatively, we could
choose (but don't) to pass an application-specific comparison
function into the heap operation functions.
-------------------------- N.B. ------------------------------FUNCTIONS
lheapAdd
l_int32 lheapAdd ( L_HEAP *lh, void *item )
lheapAdd()
Input: lheap
item to be added to the tail of the heap
Return: 0 if OK, 1 on errorlheapCreate
L_HEAP * lheapCreate ( l_int32 nalloc, l_int32 direction )
lheapCreate()
Input: size of ptr array to be alloc'd (0 for default)
direction (L_SORT_INCREASING, L_SORT_DECREASING)
Return: lheap, or null on errorlheapDestroy
void lheapDestroy ( L_HEAP **plh, l_int32 freeflag )
lheapDestroy()
Input: &lheap (<to be nulled>)
freeflag (TRUE to free each remaining struct in the array)
Return: void
Notes:
(1) Use freeflag == TRUE when the items in the array can be
simply destroyed using free. If those items require their
own destroy function, they must be destroyed before
calling this function, and then this function is called
with freeflag == FALSE.
(2) To destroy the lheap, we destroy the ptr array, then
the lheap, and then null the contents of the input ptr.lheapGetCount
l_int32 lheapGetCount ( L_HEAP *lh )
lheapGetCount()
Input: lheap
Return: count, or 0 on errorlheapPrint
l_int32 lheapPrint ( FILE *fp, L_HEAP *lh )
lheapPrint()
Input: stream
lheap
Return: 0 if OK; 1 on errorlheapRemove
void * lheapRemove ( L_HEAP *lh )
lheapRemove()
Input: lheap
Return: ptr to item popped from the root of the heap,
or null if the heap is empty or on errorlheapSort
l_int32 lheapSort ( L_HEAP *lh )
lheapSort()
Input: lh (heap, with internal array)
Return: 0 if OK, 1 on error
Notes:
(1) This sorts an array into heap order. If the heap is already
in heap order for the direction given, this has no effect.lheapSortStrictOrder
l_int32 lheapSortStrictOrder ( L_HEAP *lh )
lheapSortStrictOrder()
Input: lh (heap, with internal array)
Return: 0 if OK, 1 on error
Notes:
(1) This sorts a heap into strict order.
(2) For each element, starting at the end of the array and
working forward, the element is swapped with the head
element and then allowed to swap down onto a heap of
size reduced by one. The result is that the heap is
reversed but in strict order. The array elements are
then reversed to put it in the original order.lheapSwapDown
l_int32 lheapSwapDown ( L_HEAP *lh )
lheapSwapDown()
Input: lh (heap)
Return: 0 if OK, 1 on error
Notes:
(1) This is called after an item has been popped off the
root of the heap, and the last item in the heap has
been placed at the root.
(2) To regain the heap order, we let it bubble down,
iteratively swapping with one of its children. For a
decreasing sort, it swaps with the largest child; for
an increasing sort, the smallest. This continues until
it either reaches the lowest level in the heap, or the
parent finds that neither child should swap with it
(e.g., for a decreasing heap, the parent is larger
than or equal to both children).lheapSwapUp
l_int32 lheapSwapUp ( L_HEAP *lh, l_int32 index )
lheapSwapUp()
Input: lh (heap)
index (of array corresponding to node to be swapped up)
Return: 0 if OK, 1 on error
Notes:
(1) This is called after a new item is put on the heap, at the
bottom of a complete tree.
(2) To regain the heap order, we let it bubble up,
iteratively swapping with its parent, until it either
reaches the root of the heap or it finds a parent that
is in the correct position already vis-a-vis the child.AUTHOR
Zakariyya Mughal <zmughal@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.