Data commit

Task/Permutations-by-swapping/Jq/permutations-by-swapping-1.jq

@@ -0,0 +1,45 @@
+# The helper function, _recurse, is tail-recursive and therefore in
+# versions of jq with TCO (tail call optimization) there is no
+# overhead associated with the recursion.
+
+def permutations:
+  def abs: if . < 0 then -. else . end;
+  def sign: if . < 0 then -1 elif . == 0 then 0 else 1 end;
+  def swap(i;j): .[i] as $i | .[i] = .[j] | .[j] = $i;
+
+  # input: [ parity, extendedPermutation]
+  def _recurse:
+    .[0] as $s | .[1] as $p | (($p | length) -1) as $n
+    | [ $s, ($p[1:] | map(abs)) ],
+      (reduce range(2; $n+1) as $i
+         (0;
+          if $p[$i] < 0 and -($p[$i]) > ($p[$i-1]|abs) and -($p[$i]) > ($p[.]|abs)
+          then $i
+          else .
+          end)) as $k
+      | (reduce range(1; $n) as $i
+           ($k;
+            if $p[$i] > 0 and $p[$i] > ($p[$i+1]|abs) and $p[$i] > ($p[.]|abs)
+            then $i
+            else .
+            end)) as $k
+      | if $k == 0 then empty
+        else (reduce range(1; $n) as $i
+	       ($p;
+                if (.[$i]|abs) > (.[$k]|abs) then .[$i] *= -1
+                else .
+                end )) as $p
+        | ($k + ($p[$k]|sign)) as $i
+        | ($p | swap($i; $k)) as $p
+        | [ -($s), $p ] | _recurse
+        end ;
+
+  . as $in
+  | length as $n
+  | (reduce range(0; $n+1) as $i ([]; . + [ -$i ])) as $p
+  # recurse state: [$s, $p]
+  | [ 1, $p] | _recurse
+  | .[1] as $p
+  | .[1] = reduce range(0; $n) as $i ([]; . + [$in[$p[$i]  - 1]]) ;
+
+def count(stream): reduce stream as $x (0; .+1);

Task/Permutations-by-swapping/Jq/permutations-by-swapping-2.jq

@@ -0,0 +1,2 @@
+(["a", "b", "c"] | permutations),
+"There are \(count( [range(1;6)] | permutations )) permutations of 5 items."

Task/Permutations-by-swapping/Jq/permutations-by-swapping-3.jq

@@ -0,0 +1,9 @@
+$ jq -c -n -f Permutations_by_swapping.jq
+[1,["a","b","c"]]
+[-1,["a","c","b"]]
+[1,["c","a","b"]]
+[-1,["c","b","a"]]
+[1,["b","c","a"]]
+[-1,["b","a","c"]]
+
+"There are 32 permutations of 5 items."