branch: externals/heap
commit 9bcd8d3cc6a4ac7a96bd38a11236b0b70956f09f
Author: Toby S. Cubitt <toby-predict...@dr-qubit.org>
Commit: Toby S. Cubitt <toby-predict...@dr-qubit.org>
Added heap-build function for efficiently building a heap out of a vector.
---
heap.el | 52 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 41 insertions(+), 11 deletions(-)
diff --git a/heap.el b/heap.el
index e862809..403342d 100644
--- a/heap.el
+++ b/heap.el
@@ -67,6 +67,8 @@
;; Version 0.3
;; * converted heap data structures into defstructs
;; * increased default heap size to 16, and default resize-factor to 2
+;; * added `heap-build' function for efficiently building a heap out of
+;; a vector
;;
;; Version 0.2.2
;; * fixed bug in `heap-copy'
@@ -101,7 +103,7 @@
;;; Code:
-(provide 'heap)
+(eval-when-compile (require 'cl))
;;; ================================================================
@@ -197,6 +199,31 @@ defaulting to 2."
(heap--create compare-function initial-size resize-factor))
+(defun heap-build (compare-function vec &optional resize-factor)
+ "Build a heap from vector VEC with COMPARE-FUNCTION
+as the comparison function.
+
+Note that VEC is modified, and becomes part of the heap data
+structure. If you don't want this, copy the vector first and pass
+the copy in VEC.
+
+COMPARE-FUNCTION takes two arguments, A and B, and returns
+non-nil or nil. To implement a max-heap, it should return non-nil
+if A is greater than B. To implemenet a min-heap, it should
+return non-nil if A is less than B.
+
+RESIZE-FACTOR sets the factor by which the heap's size is
+increased if it runs out of space, defaulting to 2."
+ (or resize-factor (setq resize-factor 2))
+ (let ((heap (heap--create compare-function (length vec) resize-factor))
+ (i (ceiling (1- (expt 3
+ (ceiling (1- (log (1+ (* 2 (length vec))) 3))))) 2)))
+ (setf (heap--vect heap) vec
+ (heap--count heap) (length vec))
+ (while (>= (decf i) 0) (heap--sift-down heap i))
+ heap))
+
+
(defun heap-copy (heap)
"Return a copy of heap HEAP."
(let ((newheap (heap--create (heap--cmpfun heap) (heap--size heap)
@@ -250,17 +277,17 @@ defaulting to 2."
(defun heap-delete-root (heap)
"Return the root of the heap and delete it from the heap."
- (let (vect root (count (heap--count heap)))
+ (let ((vect (heap--vect heap))
+ root count)
;; deal with empty heaps and heaps with just one element
- (if (= count 0) nil
- (setq vect (heap--vect heap))
- (setq root (aref vect 0))
- (setf (heap--count heap) (1- (heap--count heap)))
- (if (= 1 count) (setf (heap--vect heap) (make-vector 16 nil))
- ;; Delete root, swap last element to top, and sift-down from top
- (setq vect (heap--vect heap))
- (aset vect 0 (aref vect (1- count)))
- (aset vect (1- count) nil)
+ (if (= 0 (heap--count heap)) nil
+ (setq root (aref vect 0)
+ count (decf (heap--count heap)))
+ (if (= 0 count)
+ (setf (heap--vect heap) (make-vector 16 nil))
+ ;; delete root, swap last element to top, and sift-down from top
+ (aset vect 0 (aref vect count))
+ (aset vect count nil)
(heap--sift-down heap 0))
root)))
@@ -295,6 +322,9 @@ Note that only the match highest up the heap is modified."
nil))) ; return nil if no match was found
+
+(provide 'heap)
+
;;; Local Variables:
;;; fill-column: 72
;;; End:
