Please reply to the list rather than directly to me so that other people can see the answer to my question and offer you help.
On 9 February 2014 14:04, Ni Wesley <nisp...@gmail.com> wrote: > 2014年2月9日 下午9:41于 "Oscar Benjamin" <oscar.j.benja...@gmail.com>写道： > >> On 9 February 2014 12:13, Wesley <nisp...@gmail.com> wrote: >> > Hi guys, >> > Here is one question related to algorithm. >> > Details here: >> > >> > here is input sequence like a1,a2,...,an,b1,b2,...,bn ，the ax and bx >> > always exist in pair. So, now, how to change the sequence to >> > a1,b1,...,an,bn, with time complexity as O(n) and space as O(1). >> >> Do you mean that you have a list and you want to rearrange the >> elements in-place without creating a new list? > > Yes Okay so if you're going to do it with O(1) space then it's going to have to be done with a whole bunch of swaps. Have a think with pen and paper about how you could do a sequence of swaps that would rearrange the order to the one that you want (it's actually a harder problem than it looks at first glance). This is an example of what is known as "transposition" and much information is available about algorithms for doing this in-place: http://en.wikipedia.org/wiki/In-place_matrix_transposition Oscar -- https://mail.python.org/mailman/listinfo/python-list
