Rotating an NxN matrix

I came up with the following solution for rotating an NxN matrix 90 degrees clockwise, to solve this CodeEval challenge:

Input

The first argument is a file that contains 2D N×N matrices (where 1 <= N <= 10), presented in a serialized form (starting from the upper-left element), one matrix per line. The elements of a matrix are separated by spaces.

For example:

a b c d e f g h i j k l m n o p

Output

Print to stdout matrices rotated 90° clockwise in a serialized form (same as in the input sample).

For example:

m i e a n j f b o k g c p l h d

It looks elegant to me, but can someone explain how its performance compares to the more common solutions mentioned here? Does it have \$O(n^2)\$ time complexity?

import sys, math

for line in open(sys.argv[1]):
    original = line.rstrip().replace(' ', '')
    nSquared = len(original)
    n = int(math.sqrt(nSquared))
    output = ''

    for i in range(nSquared):
        index = n * (n - 1 - i % n) + int(i / n)
        output += original[index] + ' '

    print(output.rstrip())

The expression n * (n - 1 - i % n) + int(i / n) is something I found while observing common patterns among rotated matrices.