排列组合

时间：2008-11-14 来源：jiangerji

求出s个元素中n个的所有排列情况P(s, n)
比如0,1,2的所有排列情况为012, 021, 102, 120, 201, 210,共6种情况

  def permutation(s, n):

      #从s中选取n进行排列

      if (n > len(s)) or (n <= 0) or (len(s) == 0):

          return

      if n == 1:

          for i in range(len(s)):

              yield [s[i]]

      else:

          for i in s:

              #print i, len(s), r

              st = list(s)

              st.remove(i)

              for j in permutation(st, n-1):

                  yield [i] + j

其中yield是python的生成器。

获取组合的代码为

  def combination(s, n):

      if (n > len(s)) or (n <= 0) or (len(s) == 0):

          return

      if n == 1:

          for i in s:

              yield [i]

      else:

          for i in range(len(s)):

              for j in combination(s[i+1:], n-1):

                  yield [s[i]]+j