Data update

Task/Gray-code/Jq/gray-code.jq

@@ -0,0 +1,38 @@
+def encode:
+  def flip: if . == 1 then 0 else 1 end;
+  . as $b
+  | reduce range(1; length) as $i ($b;
+     if $b[$i-1] == 1 then .[$i] |= flip
+     else .
+     end ) ;
+
+def decode:
+  def xor($a;$b): ($a + $b) % 2;
+  . as $g
+  | reduce range(1; length) as $i (.[:1];
+      .[$i] = xor($g[$i]; .[$i-1]) ) ;
+
+
+# input: a non-negative integer
+# output: a binary array, least-significant bit first
+def to_binary:
+  if . == 0 then [0]
+  else [recurse( if . == 0 then empty else ./2 | floor end ) % 2]
+    | .[:-1] # remove the uninteresting 0
+  end ;
+
+def lpad($len; $fill):
+  tostring
+  | ($len - length) as $l
+  | if $l <= 0 then .
+    else ($fill * $l)[:$l] + .
+    end;
+
+def pp: map(tostring) | join("") | lpad(5; "0");
+
+### The task
+"decimal   binary    gray  roundtrip",
+(range(0; 32) as $i
+ | ($i | to_binary | reverse) as $b
+ | ($b|encode) as $g
+ | "  \($i|lpad(2;" "))       \($b|pp)   \($g|pp)   \($g|decode == $b)" )