Programming Pearls section 2

3-otedama.py

# -*- coding: utf-8 -*-
def rotate_arr(arr, t):
    """programming peals

    rotate array algorithm(destructive)"""
    l = len(arr)
    tmp = arr[0]
    k = 0
    while True:
        j = k
        k = j+t
        if k > l-1: k -= l
        if k == 0:
            arr[j] = tmp
            break
        arr[j] = arr[k]
    return arr

a = [1,2,3,4,5]
print rotate_arr(a, 2)                  # => [3,4,5,1,2]

3-recursive.py

# -*- coding: utf-8 -*-
def rotate_arr(arr, t):
    """programming peals

    rotate array algorithm(recursive, non-destructive)"""
    if t == 0: return arr
    l = len(arr)
    if t * 2 < l:
        (a, bl, br) = (arr[:t], arr[t:l-t], arr[-t:])
        return rotate_arr(br+bl, len(br))+a
    else:
        (bl, br, a) = (arr[:l-t], arr[l-t:-l+t], arr[-l+t:])
        return a+rotate_arr(br+bl, len(br))

a = [1,2,3,4,5]
print 'start: ', a
for i in range(1,5):
    print rotate_arr(a, i)

3-simplest.py

# -*- coding: utf-8 -*-
def rotate_arr(arr, t):
    """programming peals

    rotate array algorithm(most simple)"""
    return (arr[:t][::-1]+arr[t:][::-1])[::-1] # arr[::-1] returns reversed arr

a = [1,2,3,4,5]
print 'start: ', a
for i in range(1,5):
    print rotate_arr(a, i)