Special factorials: Difference between revisions
Added Algol 68
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362880: 9
3628800: 10
</pre>
=={{header|ALGOL 68}}==
{{works with|ALGOL 68G|Any - tested with release 2.8.3.win32}}
Uses Algol 68G's LONG LONG INT with default precision, which is long enough for the values needed for the task, except exponential factorial( 5 ).
The reverse factorial function uses a UNION(INT,STRING) for the result, so the result can either be an integer or the string "undefined".
<syntaxhighlight lang="algol68">
BEGIN # show the values of some "special factorials" #
# super factorial: returns the product of the factorials up to to n #
PROC sf = ( INT n )LONG LONG INT:
BEGIN
LONG LONG INT f := 1, p := 1;
FOR i TO n DO
f *:= i;
p *:= f
OD;
p
END # sf # ;
# hyper factorial: returns the product of k^k for k up to n #
PROC hf = ( INT n )LONG LONG INT:
BEGIN
LONG LONG INT p := 1;
FOR i TO n DO
TO i DO p *:= i OD
OD;
p
END # hf # ;
# alternating factorial: returns the sum of (-1)^(i-1)*i! for i up to n #
PROC af = ( INT n )LONG LONG INT:
BEGIN
LONG LONG INT s := 0;
LONG LONG INT f := 1;
INT sign := IF ODD n THEN 1 ELSE - 1 FI;
FOR i TO n DO
f *:= i;
s +:= sign * f;
sign := - sign
OD;
s
END # hf # ;
# exponential factorial: returns n^(n-1)^(n-2)... #
PROC xf = ( INT n )LONG LONG INT:
BEGIN
LONG LONG INT x := 1;
FOR i TO n DO
LONG LONG INT ix := 1;
TO SHORTEN SHORTEN x DO ix *:= i OD;
x := ix
OD;
x
END # hf # ;
# reverse factorial: returns k if n = k! for some integer k #
# "undefined" otherwise #
PROC rf = ( LONG LONG INT n )UNION( INT, STRING ):
IF n < 2
THEN 0
ELSE
LONG LONG INT f := 1;
INT i := 1;
WHILE f < n DO
f *:= i;
i +:= 1
OD;
IF f = n THEN i - 1 ELSE "undefined" FI
FI # rf # ;
print( ( "super factorials 0..9:", newline, " " ) );
FOR i FROM 0 TO 9 DO print( ( " ", whole( sf( i ), 0 ) ) ) OD;
print( ( newline, "hyper factorials 0..9:", newline, " " ) );
FOR i FROM 0 TO 9 DO print( ( " ", whole( hf( i ), 0 ) ) ) OD;
print( ( newline, "alternating factorials 0..9:", newline, " " ) );
FOR i FROM 0 TO 9 DO print( ( " ", whole( af( i ), 0 ) ) ) OD;
print( ( newline, "exponential factorials 0..4:", newline, " " ) );
FOR i FROM 0 TO 4 DO print( ( " ", whole( xf( i ), 0 ) ) ) OD;
[]INT rf test = ( 1, 2, 6, 24, 119, 120, 720, 5040, 40320, 362880, 3628800 );
print( ( newline, "reverse factorials:", newline ) );
FOR i FROM LWB rf test TO UPB rf test DO
INT tv = rf test[ i ];
print( ( whole( tv, -8 )
, " -> "
, CASE rf( tv )
IN ( INT iv ): whole( iv, 0 )
, ( STRING sv ): sv
OUT "Unexpected value returned by rf( " + whole( tv, 0 ) + " )"
ESAC
, newline
)
)
OD
END
</syntaxhighlight>
{{out}}
<pre>
super factorials 0..9:
1 1 2 12 288 34560 24883200 125411328000 5056584744960000 1834933472251084800000
hyper factorials 0..9:
1 1 4 108 27648 86400000 4031078400000 3319766398771200000 55696437941726556979200000 21577941222941856209168026828800000
alternating factorials 0..9:
0 1 1 5 19 101 619 4421 35899 326981
exponential factorials 0..4:
1 1 2 9 262144
reverse factorials:
1 -> 0
2 -> 2
6 -> 3
24 -> 4
119 -> undefined
120 -> 5
720 -> 6
5040 -> 7
40320 -> 8
362880 -> 9
3628800 -> 10
</pre>
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