examples.py

def rotate(matrix, n):
    for layer in xrange(n/2):
        first = layer
        last = n - 1 - layer
        for i in xrange(first, last):
            offset = i - first
            top = matrix[first][i]
            # (0, 0) goes to (N-1, 0)
            matrix[first][i] = matrix[last-offset][first]
            # (0, N-1) goes to (0, 0)
            matrix[last-offset][first] = matrix[last][last - offset]
            # (0, N-1) goes to (N-1, N-1)
            matrix[last][last - offset] = matrix[i][last]
            # (N-1, N-1) goes to (0, N-1)
            matrix[i][last] = top