' Heap's algorithm non-recursive
FUNCTION permsderange (n!, flag!)
    IF n = 0 THEN permsderange = 1

    DIM a!(0 TO n), c!(0 TO n)

    FOR j = 0 TO n - 1: a(j) = j: NEXT j

    WHILE i < n
        IF c(i) < i THEN
            IF (i AND 1) = 0 THEN
                SWAP a(0), a(i)
            ELSE
                SWAP a(c(i)), a(i)
            END IF
            FOR j = 0 TO n - 1
                IF a(j) = j THEN j = 99
            NEXT j
            IF j < 99 THEN
                count = count + 1
                IF flag = 0 THEN
                    c1 = c1 + 1
                    FOR j = 0 TO n - 1
                        PRINT a(j);
                    NEXT j
                    IF c1 > 12 THEN
                        PRINT : c1 = 0
                    ELSE
                        PRINT
                    END IF
                END IF
            END IF
            c(i) = c(i) + 1
            i = 0
        ELSE
            c(i) = 0
            i = i + 1
        END IF
    WEND
    IF flag = 0 AND c1 <> 0 THEN PRINT
    permsderange = count
END FUNCTION

SUB Subfactorial (a!())
    FOR i = 0 TO UBOUND(a)
        num = num * i
        IF (i AND 1) = 1 THEN
            num = num - 1
        ELSE
            num = num + 1
        END IF
        a(i) = num
    NEXT i
END SUB

n! = 4
DIM subfac!(7)

CALL Subfactorial(subfac())

PRINT "permutations derangements for n = "; n
i! = permsderange(n, 0)
PRINT "count returned ="; i; " , !"; n; " calculated ="; subfac(n)

PRINT
PRINT "count  counted subfactorial"
PRINT "---------------------------"
FOR i = 0 TO 7
    PRINT USING " ###: ########     ########"; i; permsderange(i, 1); subfac(i)
NEXT i