上个月给cookbook发了一个排列组合算法的程序

Raymond Hattinger发了一个评论。惭愧，惭愧。水平高低真是一目了然。

----------------------------------------------------------------------------------------------------
Much simpler and clearer version, Raymond Hettinger, 2006/03/23

def perm(items, n=None):
    if n is None:
        n = len(items)
    for i in range(len(items)):
        v = items[i:i+1]
        if n == 1:
            yield v
        else:
            rest = items[:i] + items[i+1:]
            for p in perm(rest, n-1):
                yield v + p

def comb(items, n=None):
    if n is None:
        n = len(items)
    for i in range(len(items)):
        v = items[i:i+1]
        if n == 1:
            yield v
        else:
            rest = items[i+1:]
            for c in comb(rest, n-1):
                yield v + c
----------------------------------------------------------------------------------------------------

能解释一下算法吗?

在06-4-16，shhgs <shhgs.efhilt at gmail.com> 写道：
>
> 上个月给cookbook发了一个排列组合算法的程序
>
> Raymond Hattinger发了一个评论。惭愧，惭愧。水平高低真是一目了然。
>
>
> ----------------------------------------------------------------------------------------------------
> Much simpler and clearer version, Raymond Hettinger, 2006/03/23
>
> def perm(items, n=None):
>     if n is None:
>         n = len(items)
>     for i in range(len(items)):
>         v = items[i:i+1]
>         if n == 1:
>             yield v
>         else:
>             rest = items[:i] + items[i+1:]
>             for p in perm(rest, n-1):
>                 yield v + p
>
> def comb(items, n=None):
>     if n is None:
>         n = len(items)
>     for i in range(len(items)):
>         v = items[i:i+1]
>         if n == 1:
>             yield v
>         else:
>             rest = items[i+1:]
>             for c in comb(rest, n-1):
>                 yield v + c
>
> ----------------------------------------------------------------------------------------------------
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to  python-chinese-request at lists.python.cn
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>
>
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Hattinger的算法确实简单，就是递归。

排列的时候，先按顺序取一个值，然后把剩下的放到rest里面，再用递归在rest里面取n-1个值，然后把它们加起来

组合也差不多，至少拿第一个值和计算rest的时候有些不一样

On 4/16/06, Z Zarz <zarz.ml at gmail.com> wrote:
> 能解释一下算法吗?
>
> 在06-4-16，shhgs <shhgs.efhilt at gmail.com> 写道：
> >
>  上个月给cookbook发了一个排列组合算法的程序
>
> Raymond Hattinger发了一个评论。惭愧，惭愧。水平高低真是一目了然。
>
> ----------------------------------------------------------------------------------------------------
> Much simpler and clearer version, Raymond Hettinger, 2006/03/23
>
> def perm(items, n=None):
>     if n is None:
>         n = len(items)
>     for i in range(len(items)):
>         v = items[i:i+1]
>         if n == 1:
>             yield v
>         else:
>             rest = items[:i] + items[i+1:]
>             for p in perm(rest, n-1):
>                 yield v + p
>
> def comb(items, n=None):
>     if n is None:
>         n = len(items)
>     for i in range(len(items)):
>         v = items[i:i+1]
>         if n == 1:
>             yield v
>         else:
>             rest = items[i+1:]
>             for c in comb(rest, n-1):
>                 yield v + c
> ----------------------------------------------------------------------------------------------------
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to
> python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to
> python-chinese-request at lists.python.cn
> Detail Info:
> http://python.cn/mailman/listinfo/python-chinese
>
>
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to
> python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to
> python-chinese-request at lists.python.cn
> Detail Info:
> http://python.cn/mailman/listinfo/python-chinese
>
>