假設(shè)我們?cè)谟懻撆帕兄档淖值漤樞?，則可以使用兩種通用方法：
將元素的一個(gè)排列轉(zhuǎn)換為下一個(gè)排列（如ShreevatsaR發(fā)布），或者
從0向上n計(jì)數(shù)n，直接計(jì)算th排列。
對(duì)于那些不像本地人那樣講c ++的人（如我；-），可以從下面的偽代碼實(shí)現(xiàn)方法1，假設(shè)索引的零從零開(kāi)始在索引的左側(cè)為數(shù)組（用其他結(jié)構(gòu)代替） ，例如列表，是“作為練習(xí)留下的；”-）：
1. scan the array from right-to-left (indices descending from N-1 to 0)
1.1. if the current element is less than its right-hand neighbor,
call the current element the pivot,
and stop scanning
1.2. if the left end is reached without finding a pivot,
reverse the array and return
(the permutation was the lexicographically last, so its time to start over)
2. scan the array from right-to-left again,
to find the rightmost element larger than the pivot
(call that one the successor)
3. swap the pivot and the successor
4. reverse the portion of the array to the right of where the pivot was found
5. return
這是一個(gè)從CADB當(dāng)前排列開(kāi)始的示例：
1. scanning from the right finds A as the pivot in position 1
2. scanning again finds B as the successor in position 3
3. swapping pivot and successor gives CBDA
4. reversing everything following position 1 (i.e. positions 2..3) gives CBAD
5. CBAD is the next permutation after CADB
對(duì)于第二種方法（直接計(jì)算nth排列），請(qǐng)記住存在元素的N!排列N。因此，如果要排列N元素，則第一個(gè)(N-1)!排列必須以最小的元素開(kāi)始，接下來(lái)的(N-1)!排列必須以第二個(gè)最小的元素開(kāi)始，依此類推。這導(dǎo)致以下遞歸方法（再次使用偽代碼，從0開(kāi)始對(duì)排列和位置進(jìn)行編號(hào)）：
To find permutation x of array A, where A has N elements:
0. if A has one element, return it
1. set p to ( x / (N-1)! ) mod N
2. the desired permutation will be A[p] followed by
permutation ( x mod (N-1)! )
of the elements remaining in A after position p is removed
因此，例如，發(fā)現(xiàn)ABCD的第13個(gè)置換如下：
perm 13 of ABCD: {p = (13 / 3!) mod 4 = (13 / 6) mod 4 = 2; ABCD[2] = C}
C followed by perm 1 of ABD {because 13 mod 3! = 13 mod 6 = 1}
perm 1 of ABD: {p = (1 / 2!) mod 3 = (1 / 2) mod 2 = 0; ABD[0] = A}
A followed by perm 1 of BD {because 1 mod 2! = 1 mod 2 = 1}
perm 1 of BD: {p = (1 / 1!) mod 2 = (1 / 1) mod 2 = 1; BD[1] = D}
D followed by perm 0 of B {because 1 mod 1! = 1 mod 1 = 0}
B (because there's only one element)
DB
ADB
CADB
順便說(shuō)一下，元素的“刪除”可以由布爾值的并行數(shù)組表示，該數(shù)組指示哪些元素仍然可用，因此不必在每個(gè)遞歸調(diào)用上創(chuàng)建新的數(shù)組。
因此，要遍歷ABCD的排列，只需從0到23（4！-1）計(jì)數(shù)并直接計(jì)算對(duì)應(yīng)的排列即可。
