tasks a-s

Task/Permutations/ALGOL-68/permutations-1.alg

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+# Document prelude template usage:
+TEMPLATE(
+  INT upb values := 4;
+  MODE VALUE = INT;
+  FORMAT value fmt := $g(0)$
+); #
+
+MODE
+  VALVALUES = [upb values]VALUE, VALUES = REF VALVALUES,
+  YIELDVALUES = PROC(VALUES)VOID;
+
+FORMAT
+  values fmt := $"("n(upb values-1)(f(value fmt)", ")f(value fmt)")"$;
+
+# Generate permutations of the input values of valueues #
+PROC gen values permutations = (VALUES values, YIELDVALUES yield)VOID: (
+# Warning: this routine does not correctly handle duplicate elements #
+  IF LWB values = UPB values THEN
+    yield(values)
+  ELSE
+    FOR elem FROM LWB values TO UPB values DO
+      VALUE first = values[elem];
+      values[LWB values+1:elem] := values[:elem-1];
+      values[LWB values] := first;
+    # FOR VALUES next values IN # gen values permutations(values[LWB values+1:] # ) DO #,
+    ##   (VALUES next)VOID:(
+        yield(values)
+    # OD #));
+      values[:elem-1] := values[LWB values+1:elem];
+      values[elem] := first
+    OD
+  FI
+);
+
+############################################
+# Define some additional utility OPerators #
+############################################
+PRIO P = 7; # OP to calculate number of permutations #
+OP P = (INT n, k)INT: ( # n! OVER (n-k)! #
+  # ( n>k | n * ((n-1) P k) | n ); #
+  INT out := k;
+  FOR i FROM k+1 TO n DO out *:= i OD;
+  out
+);
+
+# Define an operator for doing iterations over permutations #
+PRIO DOPERM = 1;
+OP (VALUES, YIELDVALUES)VOID DOPERM = gen values permutations;
+
+# Return an a matrix of permutations #
+OP PERM = (VALUES in values)[, ]VALUE: (
+  [(UPB in values-LWB in values+1) P 1, LWB in values:UPB in values]VALUE out;
+  INT elem := LWB out;
+
+# FOR VALUES values IN # in values DOPERM (
+##   (VALUES values)VOID:(
+    out[elem, ] := values;
+    elem +:= 1
+# OD #));
+  out
+);