簡介
基本簡介
“裝錯信封問題”是由當時最有名的數學家約翰·伯努利(Johann Bernoulli,1667-1748)的兒子丹尼爾·伯努利(DanidBernoulli,1700-1782)提出來的,大意如下:
一個人寫了n封不同的信及相應的n個不同的信封,他把這n封信都裝錯了信封,問都裝錯信封的裝法有多少種?
公式證明
![全錯位排列](/img/3/504/wZwpmL2UjM1ITOwEjM5czN0UTMyITNykTO0EDMwAjMwUzLxIzLwEzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/c/1d3/wZwpmLwMDM5QDO3YzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL2MzL0QzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
n個相異的元素排成一排 。則 不在第i位的排列數為:
證明:
![全錯位排列](/img/2/3fb/wZwpmLyEzN4czN0czM2EzM1UTM1QDN5MjM5ADMwAjMwUzL3MzLxczLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![全錯位排列](/img/a/451/wZwpmLzYjM1MzN1UzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL1MzL3IzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![全錯位排列](/img/4/9b8/wZwpmL4ATOxcTNwIDN2EzM1UTM1QDN5MjM5ADMwAjMwUzLyQzLxUzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![全錯位排列](/img/8/5a7/wZwpmL1EDN1MDOyUzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL1MzLwczLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
設 的全排列 的集合為I,而使 的全排列的集合記為 ,
![全錯位排列](/img/5/52c/wZwpmLyQjM5cjM2YTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL2EzLzQzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
則 .
![全錯位排列](/img/8/013/wZwpmLwEzN3UTN2EDN2EzM1UTM1QDN5MjM5ADMwAjMwUzLxQzL1QzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
所以 .
![全錯位排列](/img/0/6c3/wZwpmL2YDNxkzM5YzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL2MzL0YzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
注意到 。
由容斥原理:
![全錯位排列](/img/4/8cd/wZwpmL4MTOxADN2YzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL2MzLyYzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
研究錯排問題的方法
枚舉法
對於情況較少的排列,可以使用枚舉法。
•當n=1時,全排列只有一種,不是錯排,D= 0。
•當n=2時,全排列有兩種,即1、2和2、1,後者是錯排,D= 1。
•當n=3時,全排列有六種,即1、2、3;1、3、2;2、1、3;2、3、1;3、1、2;3、2、1,其中只有有3、1、2和2、3、1是錯排,D=2。用同樣的方法可以知道D=9。
•最小的幾個錯排數是:D= 0,D= 1,D=2,D= 9,D= 44,D= 265,D= 1854.
遞推數列法
對於排列數較多的情況,難以採用枚舉法。這時可以用遞歸思想推導錯排數的遞迴關係式。
![全錯位排列](/img/5/d0c/wZwpmL4YzMyETN2UzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL1MzLyMzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/9/f3f/wZwpmLyMDOyAjN4QTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0EzL0QzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/e/35f/wZwpmL1UTOwATO3IDN2EzM1UTM1QDN5MjM5ADMwAjMwUzLyQzLwIzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![全錯位排列](/img/3/82a/wZwpmL1YDOzkTN0QzM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0MzL2MzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
顯然 , 。當 時,不妨設n排在了第k位,其中k≠n,也就是 。那么考慮第n位的情況。
•當k排在第n位時,除了n和k以外還有n-2個數,其錯排數為D。
•當k不排在第n位時,那么將第n位重新考慮成一個新的“第k位”,這時的包括k在內的剩下n-1個數的每一種錯排,都等價於只有n-1個數時的錯排(只是其中的第k位會換成第n位)。其錯排數為D。
所以當n排在第k位時共有D+D種錯排方法,又k有從1到n-1共n-1種取法,我們可以得到:
![全錯位排列](/img/3/6d5/wZwpmLxgTO0cDNxEjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLxIzLwQzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/3/6d5/wZwpmLxgTO0cDNxEjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLxIzLwQzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
在上面我們得到 從這個公式中我們可以推出D的通項公式,方法如下:
![全錯位排列](/img/e/172/wZwpmL2EzM3IDN3YTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL2EzLxczLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/5/db3/wZwpmL0QjN5czMyEjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLxIzLxIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
為書寫方便,記 ,則
![全錯位排列](/img/3/6d5/wZwpmLxgTO0cDNxEjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLxIzLwQzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/8/6bb/wZwpmL0ADO4EDM5QTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0EzLwYzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/d/232/wZwpmLyUTNyITMwkTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL5EzL3EzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
當n大於等於3時,由 ,即 。 所以, 。
![全錯位排列](/img/9/62d/wZwpmL2QzM3YDMzgTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL4EzL2czLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
於是有
![全錯位排列](/img/5/c00/wZwpmLzADO1YTM4QTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0EzL1IzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
將上面式子分邊累加,得
![全錯位排列](/img/3/d28/wZwpmL1QzMwQjM4cTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL3EzL2UzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
因此,我們得到錯排公式
多項式模擬
![全錯位排列](/img/9/4e4/wZwpmL2ETN1EDOxMzM2EzM1UTM1QDN5MjM5ADMwAjMwUzLzMzL1IzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/1/b32/wZwpmL1IDM1ADNyMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzL1IzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![全錯位排列](/img/5/0da/wZwpmL2ETNwUTMxEjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLxIzL0EzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/8/06a/wZwpmLwATMzkTMzETMzEzM1UTM1QDN5MjM5ADMwAjMwUzLxEzL4gzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/d/33d/wZwpmLxMTM1MDOxMzM2EzM1UTM1QDN5MjM5ADMwAjMwUzLzMzLxczLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
錯排, 需排在 、 需排在 如此類推。
![全錯位排列](/img/b/1c3/wZwpmLxcDN3cjM4QjM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0IzLyMzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![全錯位排列](/img/9/b74/wZwpmL2MTNxczM4MDN2EzM1UTM1QDN5MjM5ADMwAjMwUzLzQzL1YzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/9/c14/wZwpmLwUjMzMTM1gTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL4EzLxIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
記 ,錯排結果為 中 的係數
![全錯位排列](/img/f/a5c/wZwpmL4QTN1kDO4QTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL0EzL2IzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/c/e79/wZwpmLwcTN5ITN4IjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLyIzL2IzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
記 為基本對稱多項式,
![全錯位排列](/img/d/883/wZwpmL1QjNzYTNykzN5ADN0UTMyITNykTO0EDMwAjMwUzL5czL1AzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/f/a34/wZwpmL0IzN2UzM4AjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLwIzLyAzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![全錯位排列](/img/f/6fe/wZwpmLygDNzgTOzIjM2EzM1UTM1QDN5MjM5ADMwAjMwUzLyIzL4YzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/9/604/wZwpmLxUzN2IjN5czM2EzM1UTM1QDN5MjM5ADMwAjMwUzL3MzLwUzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/9/c14/wZwpmLwUjMzMTM1gTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL4EzLxIzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
從 選出 ,然後從 選出 ,組成
![全錯位排列](/img/d/883/wZwpmL1QjNzYTNykzN5ADN0UTMyITNykTO0EDMwAjMwUzL5czL1AzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![全錯位排列](/img/e/41f/wZwpmL2gTN1cTN5QDNzEzM1UTM1QDN5MjM5ADMwAjMwUzL0QzLzQzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![全錯位排列](/img/7/9d6/wZwpmL3QTMzcTN4ETN3kTO0UTMyITNykTO0EDMwAjMwUzLxUzLyIzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![全錯位排列](/img/3/244/wZwpmL4czMzkDN2kTM2EzM1UTM1QDN5MjM5ADMwAjMwUzL5EzL1czLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
從 選出r個x有 種可能,從 選出其餘的n-r個x有 種可能
![全錯位排列](/img/8/48b/wZwpmL4YDMzITN1UjM2EzM1UTM1QDN5MjM5ADMwAjMwUzL1IzLyQzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)