find perfect shuffle of an array, for example: 1 2 3 4 5 6 7 8 9 10 --> 1 6 2 7 3 8 4 9 5 10

PerfectShuffle.py

#!/usr/bin/python

def perfect_shuffle_(buf, left, right):
    len_ = right - left + 1
    if len_ == 2:
        return
    left_beg = left + len_ / 4
    right_beg = left + len_ / 2
    shuffle_len = len_ / 4
    if len_ % 4 == 0:
        for _ in xrange(0, shuffle_len):
            buf[left_beg], buf[right_beg] = buf[right_beg], buf[left_beg]
            left_beg += 1
            right_beg += 1
    else:
        tmp = buf[right_beg - 1]
        for _ in xrange(0, shuffle_len):
            buf[left_beg], buf[right_beg - 1] = buf[right_beg], buf[left_beg]
            left_beg += 1
            right_beg += 1
        buf[right_beg - 1] = tmp
    perfect_shuffle_(buf, left, left_beg - 1)
    perfect_shuffle_(buf, left_beg, right)

def perfect_shuffle(buf):
    if len(buf) % 2 != 0:
        return
    perfect_shuffle_(buf, 0, len(buf) - 1)

def main():
    buf = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
    perfect_shuffle(buf)
    print buf

if __name__ == '__main__':
    main()