update

Task/Hailstone-sequence/AWK/hailstone-sequence.awk

@@ -0,0 +1,29 @@
+#!/usr/bin/awk -f
+function hailstone(v, verbose) {
+	n = 1;
+	u = v;
+	while (1) {
+		if (verbose) printf " "u;
+		if (u==1) return(n);
+		n++;
+		if (u%2 > 0 )
+			u = 3*u+1;
+		else
+			u = u/2;
+	}
+}
+
+BEGIN {
+	i = 27;
+	printf("hailstone(%i) has %i elements\n",i,hailstone(i,1));
+	ix=0;
+	m=0;
+	for (i=1; i<100000; i++) {
+		n = hailstone(i,0);
+		if (m<n) {
+			m=n;
+			ix=i;
+		}
+	}
+	printf("longest hailstone sequence is %i and has %i elements\n",ix,m);
+}

Task/Hailstone-sequence/Io/hailstone-sequence.io

@@ -0,0 +1,37 @@
+makeItHail := method(n,
+  stones := list(n)
+  while (n != 1,
+    if(n isEven,
+      n = n / 2,
+      n = 3 * n + 1
+    )
+    stones append(n)
+  )
+)
+
+out := makeItHail(27)
+writeln("For the sequence beginning at 27, the number of elements generated is ", out size, ".")
+write("The first four elements generated are ")
+for(i, 0, 3,
+  write(out at(i), " ")
+)
+writeln(".")
+
+write("The last four elements generated are ")
+for(i, out size - 4, out size - 1,
+  write(out at(i), " ")
+)
+writeln(".")
+
+numOfElems := 0
+nn := 3
+for(x, 3, 100000,
+  out = makeItHail(x)
+  if(out size > numOfElems,
+    numOfElems = out size
+    nn = x
+  )
+)
+
+writeln("For numbers less than or equal to 100,000, ", nn,
+" has the longest sequence of ", numOfElems, " elements.")

Task/Hailstone-sequence/Racket/hailstone-sequence.rkt

@@ -1,19 +1,20 @@
 #lang racket
-(define memo (make-hash))
-(hash-set! memo 1 '((1) 1))
 
-(define (hailstone n)
-  (hash-ref memo n
-   (λ ()
-     (define h (hailstone (if (even? n) (/ n 2) (+ (* 3 n) 1))))
-     (hash-set! memo n (list (cons n (first h)) (+ (second h) 1)))
-     (hash-ref memo n))))
+(define hailstone
+  (let ([t (make-hasheq)])
+    (hash-set! t 1 '(1))
+    (λ(n) (hash-ref! t n
+            (λ() (cons n (hailstone (if (even? n) (/ n 2) (+ (* 3 n) 1)))))))))
 
-(define h27 (first (hailstone 27)))
+(define h27 (hailstone 27))
+(printf "h(27) = ~s, ~s items\n"
+        `(,@(take h27 4) ... ,@(take-right h27 4))
+        (length h27))
 
-(printf "first 4 elements of h(27): ~v\n" (take h27 4))
-(printf "last  4 elements of h(27): ~v\n" (take-right h27 4))
-
-(printf "x < 10000 such that h(x) gives the longest sequence: ")
-(for/fold ([m 0]) ([n (in-range 1 100000)])
-  (max m (second (hailstone n))))
+(define N 100000)
+(define longest
+  (for/fold ([m #f]) ([i (in-range 1 (add1 N))])
+    (define h (hailstone i))
+    (if (and m (> (cdr m) (length h))) m (cons i (length h)))))
+(printf "for x<=~s, ~s has the longest sequence with ~s items\n"
+        N (car longest) (cdr longest))