- COPYRIGHT AND LICENSE
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. ------------------------------
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 error
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 error
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.
l_int32 lheapGetCount ( L_HEAP *lh )
lheapGetCount() Input: lheap Return: count, or 0 on error
l_int32 lheapPrint ( FILE *fp, L_HEAP *lh )
lheapPrint() Input: stream lheap Return: 0 if OK; 1 on error
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 error
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.
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.
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).
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.
Zakariyya Mughal <email@example.com>
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.