回溯（b a c k t r a c k i n g）是一種系統地搜索問題解答的方法。為了實現回溯，首先需要為問題定義一個解空間（ solution space），這個空間必須至少包含問題的一個解（可能是最優的）。在迷宮老鼠問題中，我們可以定義一個包含從入口到出口的所有路徑的解空間；在具有n 個對象的0 / 1背包問題中（見1 . 4節和2 . 2節），解空間的一個合理選擇是2n 個長度為n 的0 / 1向量的集合，這個集合表示了將0或1分配給x的所有可能方法。當n= 3時，解空間為{ ( 0 , 0 , 0 )，( 0 , 1 , 0 )，( 0 , 0 , 1 )，( 1 , 0 , 0 )，( 0 , 1 , 1 )，( 1 , 0 , 1 )，( 1 , 1 , 0 )，( 1 , 1 , 1 ) }。
標簽：
搜索
上傳時間：
2014-01-17
上傳用戶：jhksyghr
The government of a small but important country has decided that the alphabet needs to be streamlined and reordered. Uppercase letters will be eliminated. They will issue a royal decree in the form of a String of B and A characters. The first character in the decree specifies whether a must come ( B )Before b in the new alphabet or ( A )After b . The second character determines the relative placement of b and c , etc. So, for example, "BAA" means that a must come Before b , b must come After c , and c must come After d .
Any letters beyond these requirements are to be excluded, so if the decree specifies k comparisons then the new alphabet will contain the first k+1 lowercase letters of the current alphabet.
Create a class Alphabet that contains the method choices that takes the decree as input and returns the number of possible new alphabets that conform to the decree. If more than 1,000,000,000 are possible, return -1.
Definition
標簽：
government
streamline
important
alphabet
上傳時間：
2015-06-09
上傳用戶：weixiao99
