/*
* UCW Library -- Universal Heap Macros
*
- * (c) 2001 Martin Mares <mj@ucw.cz>
- * (c) 2005 Tomas Valla <tom@ucw.cz>
+ * (c) 2001--2012 Martin Mares <mj@ucw.cz>
+ * (c) 2005--2012 Tomas Valla <tom@ucw.cz>
*
* This software may be freely distributed and used according to the terms
* of the GNU Lesser General Public License.
*
* The first element `heap[1]` is always lower or equal to all other elements.
*
+ * Position tracking
+ * -----------------
+ *
+ * As a heap does not support efficient lookup of an element by value, all functions
+ * acting on existing heap elements need to obtain the position of the element in the
+ * heap. This position has to be tracked by the caller, usually in the supplied swap
+ * callback.
+ *
+ * However, there are some caveats noted in the descriptions of individual functions.
+ *
* [[macros]]
* Macros
* ------
***/
-/* For internal usage. */
+/* For internal use. */
#define HEAP_BUBBLE_DOWN_J(heap,num,less,swap) \
for (;;) \
{ \
_j = _l; \
}
-/* For internal usage. */
+/* For internal use. */
#define HEAP_BUBBLE_UP_J(heap,num,less,swap) \
while (_j > 1) \
{ \
}
/**
- * Shuffle the unordered array @heap of @num elements to become a valid heap. The time complexity is linear.
+ * Shuffle the items `heap[1]`, ..., `heap[num]` to get a valid heap.
+ * This operation takes linear time.
+ *
+ * Position tracking: Position of `heap[i]` must be initialized to `i` before calling.
**/
#define HEAP_INIT(type,heap,num,less,swap) \
do { \
} while(0)
/**
- * Delete the minimum element `heap[1]` in `O(log(n))` time.
+ * Delete the minimum element `heap[1]` in `O(log(n))` time. The @num variable is decremented.
* The removed value is moved just after the resulting heap (`heap[num + 1]`).
+ *
+ * Position tracking: Fully automatic.
**/
-#define HEAP_DELMIN(type,heap,num,less,swap) \
+#define HEAP_DELETE_MIN(type,heap,num,less,swap) \
do { \
uns _j, _l; \
type x; \
} while(0)
/**
- * Insert `heap[num + 1]` in `O(log(n))` time.
+ * Insert a new element @elt to the heap. The @num variable is incremented.
+ * This operation takes `O(log(n))` time.
+ *
+ * Position tracking: The position of the new element must be initialized to @num+1
+ * before calling this macro.
**/
-#define HEAP_INSERT(type,heap,num,less,swap) \
+#define HEAP_INSERT(type,heap,num,less,swap,elt) \
do { \
uns _j, _u; \
type x; \
+ heap[++num] = elt; \
_j = num; \
HEAP_BUBBLE_UP_J(heap,num,less,swap); \
} while(0)
/**
- * If you need to increase the value of `heap[pos]`, just do it and then call this macro to rebuild the heap.
- * Only `heap[pos]` can be changed, the rest of the array must form a valid heap.
+ * Increase `heap[pos]` to a new value @elt (greater or equal to the previous value).
* The time complexity is `O(log(n))`.
+ *
+ * Position tracking: Fully automatic.
**/
-#define HEAP_INCREASE(type,heap,num,less,swap,pos) \
+#define HEAP_INCREASE(type,heap,num,less,swap,pos,elt) \
do { \
uns _j, _l; \
type x; \
+ heap[pos] = elt; \
_j = pos; \
HEAP_BUBBLE_DOWN_J(heap,num,less,swap); \
} while(0)
/**
- * Delete `heap[pos]` in `O(log(n))` time.
+ * Decrease `heap[pos]` to a new value @elt (less or equal to the previous value).
+ * The time complexity is `O(log(n))`.
+ *
+ * Position tracking: Fully automatic.
+ **/
+#define HEAP_DECREASE(type,heap,num,less,swap,pos,elt) \
+ do { \
+ uns _j, _u; \
+ type x; \
+ heap[pos] = elt; \
+ _j = pos; \
+ HEAP_BUBBLE_UP_J(heap,num,less,swap); \
+ } while(0)
+
+/**
+ * Change `heap[pos]` to a new value @elt. The time complexity is `O(log(n))`.
+ * If you know that the new value is always smaller or always greater, it is faster
+ * to use `HEAP_DECREASE` or `HEAP_INCREASE` respectively.
+ *
+ * Position tracking: Fully automatic.
+ **/
+#define HEAP_REPLACE(type,heap,num,less,swap,pos,elt) \
+ do { \
+ type _elt = elt; \
+ if (less(heap[pos], _elt)) \
+ HEAP_INCREASE(type,heap,num,less,swap,pos,_elt); \
+ else \
+ HEAP_DECREASE(type,heap,num,less,swap,pos,_elt); \
+ } while(0)
+
+/**
+ * Replace the minimum `heap[pos]` by a new value @elt. The time complexity is `O(log(n))`.
+ *
+ * Position tracking: Fully automatic.
+ **/
+#define HEAP_REPLACE_MIN(type,heap,num,less,swap,elt) \
+ HEAP_INCREASE(type,heap,num,less,swap,1,elt)
+
+/**
+ * Delete an arbitrary element, given by its position. The @num variable is decremented.
+ * The operation takes `O(log(n))` time.
+ *
+ * Position tracking: Fully automatic.
**/
#define HEAP_DELETE(type,heap,num,less,swap,pos) \
do { \
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