programming-pearls-column2-problem3.py

def rotstring( input_string, rotate_distance ):
    string_length = len(input_string)
    print "input: " + input_string
    print "rotate_distance: " + str(rotate_distance)
    print "string_length: " + str(string_length)

    if rotate_distance == 0 or rotate_distance == string_length:
        print "Rotate distance is 0 or rotate distance = string length, exiting"
        return

    p = rotate_distance
    print "p(rotate distance): " + str(p)

    i = rotate_distance
    print "i(rotate distance): " + str(i)

    j = string_length - p
    print "j(string length - p(rotate distance)): " + str(j)


    while i != j:
        print "while i(" + str(i) + ") != j(" + str(j) + ")"
        if i > j:
                print "i > j"
                input_string = swap(input_string, p-i, p, j)
                print "swap( p(" + str(p) + ")-i(" + str(i) + "), p(" + str(p) + "), j(" + str(j) + ") )"
                print "swap result: " + input_string
                i -= j
        else:
                print "i <= j"
                input_string = swap(input_string, p-i, p+j-i, i)
                print "swap( p(" + str(p) + ")-i(" + str(i) + "), p(" + str(p) + ")+j(" + str(j) + ")-i(" + str(i) + "), i(" + str(i) + ") )"
                print "swap result: " + input_string
                j -= i
    input_string = swap(input_string, p-i, p, i)
    print "final swap( p(" + str(p) + ")-i(" + str(i) + "), p(" + str(p) + "), i(" + str(i) + ") )"

    return input_string

def swap(input_string, i, j, k):
    # exchanges x[i..i+k-1] with x[j..j+k-1]
    # swap("abcd", 0, 3, 1) -> dbca
    while k > 0:
        temp = input_string[i]

        string_list = list(input_string)
        string_list[i] = input_string[j]
        string_list[j] = temp
        input_string = ''.join(string_list)

        i += 1
        j += 1
        k -= 1
    return input_string

print rotstring( "ab", 1)
#print swap("abcd", 0, 3, 1)