String cyclic LeftShift (String s, int k) that creates and returns a string in which character of s has been moved left k steps, so that the characters that would "fall off' the left end are appended to the right.
For example, when called with the parameters ("Hello world ", 3), the method would return "1o worldHel".
Design your method so that it works quickly even if k is greater than the length of s, maybe even as large as +1,000,000,000.