彻底搞懂错排公式 彻底搞懂错排公式

彻底搞懂错排公式

问题:现有10本书按照顺序摆放,现要求重新排列,使得新的书的顺序中每一本书都不在原来的位置,求有多少种排列方式?

这个问题推广一下,就是错排问题,是组合数学中的问题之一。考虑一个有n个元素的排列,若一个排列中所有的元素都不在自己原来的位置上,那么这样的排列就称为原排列的一个错排。 n个元素的错排数记为D(n)。 研究一个排列错排个数的问题,叫做错排问题或称为更列问题

OK,现在详细分析这个问题,我们要的最终结果就是书的编号与所在位置的编号不同,在这里,我们把n本书的错排操作数记为D(n),那n-1本就是D(n-1),n-2本就是D(n-2)啦,下面,我们把放置问题分为两步(初始位置号与书的编号相同):

第一步:

        我们取一本书,书的编号为m,现在这本书就在我们手中,注意,按照题目要求,最开始的时候这本书的位置号也是m号,按照题目要求,我们现在放书时不能放回这个位置m了,而是要选择其他位置,那么有多少种选择呢,想一下,总共有n本书,n个位置,现在我手里这本书不能把它放到位置m,那么剩下的n-1个位置我当然就是随便扔啦,也就是n-1种扔法,好,现在,我选择了位置k,我决定把手里这本书放到位置k这里,记住这个是位置编号k,那么,我肯定要把原来这里的编号为k的书拿出来,再把这本编号为n的书放进去喽。所以,现在我们手里的书的编号是k

第二步:

        我们把手里这本编号为k的书本放到书架,注意,放的过程中我们又面临两种情况,可以想到,此时此刻现在书架上编号m的位置是空着的,所以我们可以选择放在这个位置上,书的编号为k,位置编号为m,没错,满足题意,这是第一种情况,还有一种就是我不选择这个空着的位置m,我再重新选择一个新的位置,我们称之为第二种情况,下面详细分析

第一种情况:我把这本编号为k的书放到这个编号为m的地址,那现在我们面前是什么状况呢,就是位置k和位置m的书交换位置,也就是位置号不等于书号,即满足错排,总共n个位置,我们只动了m和k这两个位置,那么剩下的n-2个位置还是纹丝不动,保持一一对应的关系呢,那么对于剩下的这n-2本书的错排操作,我们又回到了问题的起点,求n-2本的错排操作数D(n-2),结合第一步,我们可以得到第一种情况总共有(n-1)*D(n-2)种方法

第二种情况:我们不选择这个空着的位置m啦,我们手持这本编号为k的书,我们从除了位置m以及位置k的剩下的n-2个位置中选择一个位置,OK,我们现在开始想,我手里这本书不能放在这个位置m,嗯嗯,除了第一步我们放置的那本书m不用管了,我们还要搞手里这本和剩下的n-2本,也就是n-1本,同时又要求手里这本k还不能放到位置m,这是不是就相当于把手里这本加上剩下的n-2本也就是n-1本书进行错排呢,哇哇哇,想一想,错排的定义,要求每本书都不能呆在某一个特定位置,是不是刚好符合呢qwq,所以,现在的为题就到了求手里这本和剩下的n-2本总共是n-1本书的错排操作数,我们记为D(n-1),结合第一步,我们得出这第二种情况共有(n-1)*D(n-1)种方法

好的,现在我们总结两种情况,结果进行相加,就可以得到递推公式啦

递推公式为:\large {\color{Red} D(n)=(n-1)*[D(n-1)+D(n-2)]}

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">qq_41747892</span></a><span class="date" title="2019-07-23 16:39:38">8个月前</span><span class="floor-num"></span><span class="new-comment" style="display:inline-block;margin-top:0px">不错</span><span class="new-opt-box"><a class="btn btn-link-blue btn-report" data-type="report">举报</a><a class="btn btn-link-blue btn-reply" data-type="reply">回复</a></span></div><div class="comment-like " data-commentid="10233355"><svg t="1569296798904" class="icon " viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5522" width="200" height="200"><path d="M726.016 906.666667h-348.586667a118.016 118.016 0 0 1-116.992-107.904l-29.013333-362.666667A117.589333 117.589333 0 0 1 348.458667 309.333333H384c126.549333 0 160-104.661333 160-160 0-51.413333 39.296-88.704 93.397333-88.704 36.906667 0 71.68 18.389333 92.928 49.194667 26.88 39.04 43.178667 111.658667 12.714667 199.509333h95.530667a117.418667 117.418667 0 0 1 115.797333 136.106667l-49.28 308.522667a180.608 180.608 0 0 1-179.072 152.704zM348.458667 373.333333l-4.48 0.170667a53.461333 53.461333 0 0 0-48.768 57.472l29.013333 362.666667c2.218667 27.52 25.6 49.024 53.205333 49.024h348.544a116.949333 116.949333 0 0 0 115.925334-98.816l49.322666-308.736a53.418667 53.418667 0 0 0-52.650666-61.781334h-144.085334a32 32 0 0 1-28.458666-46.634666c45.909333-89.130667 28.885333-155.434667 11.562666-180.522667a48.981333 48.981333 0 0 0-40.192-21.504c-6.912 0-29.397333 1.792-29.397333 24.704 0 111.317333-76.928 224-224 224h-35.541333zM170.624 906.666667a32.042667 32.042667 0 0 1-31.872-29.44l-42.666667-533.333334a32.042667 32.042667 0 0 1 29.354667-34.474666c17.066667-1.408 33.024 11.733333 34.432 29.354666l42.666667 533.333334a32.042667 32.042667 0 0 1-31.914667 34.56z" p-id="5523"></path></svg><span></span></div></div></li></ul><ul class="comment-list"><li class="comment-line-box d-flex" data-commentid="10174513" data-replyname="qq_43408238">      <a target="_blank" href="https://me.csdn.net/qq_43408238"><img src="https://profile.csdnimg.cn/9/B/7/3_qq_43408238" username="qq_43408238" alt="qq_43408238" class="avatar"></a>        <div class="right-box ">          <div class="new-info-box clearfix">            <a target="_blank" href="https://me.csdn.net/qq_43408238"><span class="name ">冷血怪兽</span></a><span class="date" title="2019-07-15 10:08:58">8个月前</span><span class="floor-num"></span><span class="new-comment" style="display:inline-block;margin-top:0px">不错</span><span class="new-opt-box"><a class="btn btn-link-blue btn-report" data-type="report">举报</a><a class="btn btn-link-blue btn-reply" data-type="reply">回复</a></span></div><div class="comment-like " data-commentid="10174513"><svg t="1569296798904" class="icon " viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5522" width="200" height="200"><path d="M726.016 906.666667h-348.586667a118.016 118.016 0 0 1-116.992-107.904l-29.013333-362.666667A117.589333 117.589333 0 0 1 348.458667 309.333333H384c126.549333 0 160-104.661333 160-160 0-51.413333 39.296-88.704 93.397333-88.704 36.906667 0 71.68 18.389333 92.928 49.194667 26.88 39.04 43.178667 111.658667 12.714667 199.509333h95.530667a117.418667 117.418667 0 0 1 115.797333 136.106667l-49.28 308.522667a180.608 180.608 0 0 1-179.072 152.704zM348.458667 373.333333l-4.48 0.170667a53.461333 53.461333 0 0 0-48.768 57.472l29.013333 362.666667c2.218667 27.52 25.6 49.024 53.205333 49.024h348.544a116.949333 116.949333 0 0 0 115.925334-98.816l49.322666-308.736a53.418667 53.418667 0 0 0-52.650666-61.781334h-144.085334a32 32 0 0 1-28.458666-46.634666c45.909333-89.130667 28.885333-155.434667 11.562666-180.522667a48.981333 48.981333 0 0 0-40.192-21.504c-6.912 0-29.397333 1.792-29.397333 24.704 0 111.317333-76.928 224-224 224h-35.541333zM170.624 906.666667a32.042667 32.042667 0 0 1-31.872-29.44l-42.666667-533.333334a32.042667 32.042667 0 0 1 29.354667-34.474666c17.066667-1.408 33.024 11.733333 34.432 29.354666l42.666667 533.333334a32.042667 32.042667 0 0 1-31.914667 34.56z" p-id="5523"></path></svg><span></span></div></div></li></ul><ul class="comment-list"><li class="comment-line-box d-flex" data-commentid="10132169" data-replyname="han1202012">      <a target="_blank" href="https://me.csdn.net/han1202012"><img src="https://profile.csdnimg.cn/5/4/2/3_han1202012" username="han1202012" alt="han1202012" class="avatar"></a>        <div class="right-box ">          <div class="new-info-box clearfix">            <a target="_blank" href="https://me.csdn.net/han1202012"><span class="name ">韩曙亮</span></a><span class="date" title="2019-07-08 15:21:05">9个月前</span><span class="floor-num"></span><span class="new-comment" style="display:inline-block;margin-top:0px">很详细 已经写出了递推方程</span><span class="new-opt-box"><a class="btn btn-link-blue btn-report" data-type="report">举报</a><a class="btn btn-link-blue btn-reply" data-type="reply">回复</a></span></div><div class="comment-like " data-commentid="10132169"><svg t="1569296798904" class="icon " viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5522" width="200" height="200"><path d="M726.016 906.666667h-348.586667a118.016 118.016 0 0 1-116.992-107.904l-29.013333-362.666667A117.589333 117.589333 0 0 1 348.458667 309.333333H384c126.549333 0 160-104.661333 160-160 0-51.413333 39.296-88.704 93.397333-88.704 36.906667 0 71.68 18.389333 92.928 49.194667 26.88 39.04 43.178667 111.658667 12.714667 199.509333h95.530667a117.418667 117.418667 0 0 1 115.797333 136.106667l-49.28 308.522667a180.608 180.608 0 0 1-179.072 152.704zM348.458667 373.333333l-4.48 0.170667a53.461333 53.461333 0 0 0-48.768 57.472l29.013333 362.666667c2.218667 27.52 25.6 49.024 53.205333 49.024h348.544a116.949333 116.949333 0 0 0 115.925334-98.816l49.322666-308.736a53.418667 53.418667 0 0 0-52.650666-61.781334h-144.085334a32 32 0 0 1-28.458666-46.634666c45.909333-89.130667 28.885333-155.434667 11.562666-180.522667a48.981333 48.981333 0 0 0-40.192-21.504c-6.912 0-29.397333 1.792-29.397333 24.704 0 111.317333-76.928 224-224 224h-35.541333zM170.624 906.666667a32.042667 32.042667 0 0 1-31.872-29.44l-42.666667-533.333334a32.042667 32.042667 0 0 1 29.354667-34.474666c17.066667-1.408 33.024 11.733333 34.432 29.354666l42.666667 533.333334a32.042667 32.042667 0 0 1-31.914667 34.56z" p-id="5523"></path></svg><span></span></div></div></li></ul><ul class="comment-list"><li class="comment-line-box d-flex" data-commentid="9993591" data-replyname="weixin_44126603">      <a target="_blank" href="https://me.csdn.net/weixin_44126603"><img src="https://profile.csdnimg.cn/3/0/F/3_weixin_44126603" username="weixin_44126603" alt="weixin_44126603" class="avatar"></a>        <div class="right-box ">          <div class="new-info-box clearfix">            <a target="_blank" href="https://me.csdn.net/weixin_44126603"><span class="name ">尼可羊</span></a><span class="date" title="2019-06-17 09:28:33">9个月前</span><span class="floor-num"></span><span class="new-comment" style="display:inline-block;margin-top:0px">博主讲的太好啦!</span><span class="new-opt-box"><a class="btn btn-link-blue btn-report" data-type="report">举报</a><a class="btn btn-link-blue btn-reply" data-type="reply">回复</a></span></div><div class="comment-like " data-commentid="9993591"><svg t="1569296798904" class="icon " viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5522" width="200" height="200"><path d="M726.016 906.666667h-348.586667a118.016 118.016 0 0 1-116.992-107.904l-29.013333-362.666667A117.589333 117.589333 0 0 1 348.458667 309.333333H384c126.549333 0 160-104.661333 160-160 0-51.413333 39.296-88.704 93.397333-88.704 36.906667 0 71.68 18.389333 92.928 49.194667 26.88 39.04 43.178667 111.658667 12.714667 199.509333h95.530667a117.418667 117.418667 0 0 1 115.797333 136.106667l-49.28 308.522667a180.608 180.608 0 0 1-179.072 152.704zM348.458667 373.333333l-4.48 0.170667a53.461333 53.461333 0 0 0-48.768 57.472l29.013333 362.666667c2.218667 27.52 25.6 49.024 53.205333 49.024h348.544a116.949333 116.949333 0 0 0 115.925334-98.816l49.322666-308.736a53.418667 53.418667 0 0 0-52.650666-61.781334h-144.085334a32 32 0 0 1-28.458666-46.634666c45.909333-89.130667 28.885333-155.434667 11.562666-180.522667a48.981333 48.981333 0 0 0-40.192-21.504c-6.912 0-29.397333 1.792-29.397333 24.704 0 111.317333-76.928 224-224 224h-35.541333zM170.624 906.666667a32.042667 32.042667 0 0 1-31.872-29.44l-42.666667-533.333334a32.042667 32.042667 0 0 1 29.354667-34.474666c17.066667-1.408 33.024 11.733333 34.432 29.354666l42.666667 533.333334a32.042667 32.042667 0 0 1-31.914667 34.56z" p-id="5523"></path></svg><span></span></div></div></li></ul><ul class="comment-list"><li class="comment-line-box d-flex" data-commentid="9678763" data-replyname="weixin_43736492">      <a target="_blank" href="https://me.csdn.net/weixin_43736492"><img src="https://profile.csdnimg.cn/B/0/5/3_weixin_43736492" username="weixin_43736492" alt="weixin_43736492" class="avatar"></a>        <div class="right-box ">          <div class="new-info-box clearfix">            <a target="_blank" href="https://me.csdn.net/weixin_43736492"><span class="name ">深入人心</span></a><span class="date" title="2019-05-01 11:56:05">11个月前</span><span class="floor-num"></span><span class="new-comment" style="">我们把手里这本编号为k的书本放到书架,注意,放的过程中我们又面临两种情况,可以想到,此时此刻现在书架上编号m的位置是空着的,所以我们可以选择放在这个位置上,书的编号为k,位置编号为m,

题目不是要求每一本书都和原来的书的位置相同,现在不仅仅满足2本书的位置不相同而已嘛举报回复


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问题:现有10本书按照顺序摆放,现要求重新排列,使得新的书的顺序中每一本书都不在原来的位置,求有多少种排列方式?

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