Permutation

Code

def permute(A, p, n):
    if n == 1:
        return [(A[p],)]
    else:
        B = permute(A, p+1, n-1)
        return [insertHelper(x, i, A[p]) for i in range(n) for x in B]

def insertHelper(x, i, m):
    x = list(x)
    x.insert(i, m)
    return tuple(x)

def main():
    A = [3, 1, 2]
    print('the permutation of A is: ', permute(A, 0, len(A)))

main()

Mathematical formula

![][1]
[1]: http://latex.codecogs.com/svg.latex?A_n=n!

![][2]
[2]: http://latex.codecogs.com/svg.latex?A_n^m=\frac{n!}{(n-m)!}