# File: perm.py
# Author: San Skulrattanakulchai

def permutation(n):

    '''
    Precondition: Assuming array A[0..n-1] is a permutation of [n],
      and k is some integer between 0 and n-1 inclusive.
    perm(k) will generate all permutation of the subarray A[k..n-1]
    but fixing A[0..k-1], and for each permutation (of A itself),
    prints it out.
    '''
    def perm(k):
        if k == n:
            print(A)
        else:
            for i in range(k, n):
                A[i], A[k] = A[k], A[i]
                perm(k+1)
                A[i], A[k] = A[k], A[i]

    A = list(range(n))
    perm(0)

###################### Testing ######################
permutation(4)