*

1 files changed, 61 insertions, 0 deletions

diff --git a/js/games/nluqo.github.io/~bh/61a-pages/Lib/huffman.scm b/js/games/nluqo.github.io/~bh/61a-pages/Lib/huffman.scm
new file mode 100644
index 0000000..728b100
--- /dev/null
+++ b/js/games/nluqo.github.io/~bh/61a-pages/Lib/huffman.scm
@@ -0,0 +1,61 @@
+(define (make-leaf symbol weight)
+   (list 'leaf symbol weight))
+
+(define (leaf? object)
+   (eq? (car object) 'leaf))
+
+(define (symbol-leaf x) (cadr x))
+
+(define (weight-leaf x) (caddr x))
+
+(define (make-code-tree left right)
+   (list left
+         right
+         (append (symbols left) (symbols right))
+         (+ (weight left) (weight right))))
+
+(define (left-branch tree) (car tree))
+
+(define (right-branch tree) (cadr tree))
+
+(define (symbols tree)
+   (if (leaf? tree)
+       (list (symbol-leaf tree))
+       (caddr tree)))
+
+(define (weight tree)
+   (if (leaf? tree)
+       (weight-leaf tree)
+       (cadddr tree)))
+
+(define (adjoin-set x set)
+   (cond ((null? set) (list x))
+         ((< (weight x) (weight (car set))) (cons x set))
+         (else (cons (car set)
+                     (adjoin-set x (cdr set))))))
+
+(define (make-leaf-set pairs)
+   (if (null? pairs)
+       '()
+       (let ((pair (car pairs)))
+         (adjoin-set (make-leaf (car pair)     ;symbol
+                                (cadr pair))   ;frequency
+                     (make-leaf-set (cdr pairs))))))
+
+(define (decode bits tree)
+  (decode-1 bits tree tree))
+
+(define (decode-1 bits tree current-branch)
+  (if (null? bits)
+      '()
+      (let ((next-branch
+             (choose-branch (car bits) current-branch)))
+        (if (leaf? next-branch)
+            (cons (symbol-leaf next-branch)
+                  (decode-1 (cdr bits) tree tree))
+            (decode-1 (cdr bits) tree next-branch)))))
+
+(define (choose-branch bit branch)
+  (cond ((= bit 0) (left-branch branch))
+        ((= bit 1) (right-branch branch))
+        (else (error "bad bit -- CHOOSE-BRANCH" bit))))