每日算法题: Look and Say Sequence

Hi, here's your problem today. This problem was recently asked by Google:

A look-and-say sequence is defined as the integer sequence beginning with a single digit in which the next term is obtained by describing the previous term. An example is easier to understand:

Each consecutive value describes the prior value.

1      #

11     # one 1's

21     # two 1's

1211   # one 2, and one 1.

111221 # #one 1, one 2, and two 1's.

Your task is, return the nth term of this sequence.