Data commit

Task/Hofstadter-Q-sequence/Icon/hofstadter-q-sequence.icon

@@ -0,0 +1,39 @@
+link printf
+
+procedure main()
+
+V := [1, 1, 2, 3, 3, 4, 5, 5, 6, 6]
+every i := 1 to *V do
+   if Q(i) ~= V[i] then stop("Assertion failure for position ",i)
+printf("Q(1 to %d) - verified.\n",*V)
+
+q := Q(n := 1000)
+v := 502
+printf("Q[%d]=%d - %s.\n",n,v,if q = v then "verified" else "failed")
+
+invcount := 0
+every i := 2 to (n := 100000) do
+   if Q(i) < Q(i-1) then {
+      printf("Q(%d)=%d < Q(%d)=%d\n",i,Q(i),i-1,Q(i-1))
+      invcount +:= 1
+      }
+printf("There were %d inversions in Q up to %d\n",invcount,n)
+end
+
+
+
+procedure Q(n) #: Hofstader Q sequence
+static S
+initial S := [1,1]
+
+if q := S[n] then return q
+else {
+   q := Q(n - Q(n - 1)) + Q(n - Q(n - 2))
+   if *S = n - 1 then {
+      put(S,q)
+      return q
+      }
+   else
+      runerr(500,n)
+   }
+end