[Algorithm 15] full string Arrangement

Topic: enter a string to print all the arrays of the string. For example, input string ABC and output all columns as ABC, ACB, Bac, BCA, cab, and CBA.

 

[Thinking path] let's think about it. If we don't do programming or do it manually, We will basically consider: first fix a letter each time and then arrange the remaining letters in full; then change to a fixed letter, and then arrange the rest of the letters in full. This is just a loop. In other words: assume that the string with a length of N is arranged in the F (n) mode, then our basic idea is to make one of the N letters start each time ", the other n-1 letters are arranged in the F (n-1) format. In this way, we can see that this is obviously a recursive idea.

What is the most important condition for recursion? Or, what is the minimum subproblem? The above ABC example shows that the first step is to fix a and then arrange BC; then arrange BC as a sub-problem, which is also fixed as B and C; then arrange C as a sub-problem, and fix C, there is one character string terminator ('\ 0'); when it comes to the Terminator, all the preceding characters are arranged, so we only need to print all the previous fixed characters.

Based on this idea, we can easily get the followingCode:

 1 # Include <iostream>
 2 # Include < String >
 3   Using  Namespace STD;
 4  
 5   Void Stringpermutation ( Char * STR, Char * Perbegin)
 6 {
 7       If (STR = NULL | perbegin = NULL)
 8           Return ;
 9  
10       //  If the start position is the ending character, print all characters before the ending character  
  11       If (* Perbegin = '  \ 0  ' )
 12 {
 13 Cout <STR <Endl;
 14 }
 15       Else 
16 {
 17      
 18           For ( Char * PCH = perbegin; * PCH! = '  \ 0  ' ; ++ PCH)
 19 {
 20               //  Place where the nth character and the first character are exchanged  
  21              Char Temp = * PCH;
 22 * PCH = * perbegin;
 23 * Perbegin = temp;
 24  
 25               //  Sort all characters after the first character  
  26 Stringpermutation (STR, perbegin + 1 );
 27  
 28              //  Exchange the nth character with the first character  
  29 Temp = * PCH;
 30 * PCH = * perbegin;
 31 * Perbegin = temp;
 32 }
 33 }
 34 }
 35  
 36   Void Stringpermutation ( Char * String )
 37 {
 38 Stringpermutation ( String , String );
 39 }
 40  
 41   Int Main ()
 42 {
 43      Char P [] = "  ABC  " ;
 44  
 45 Stringpermutation (P );
 46      
 47       Return   0 ;
 48 }

The running result is as follows:

[Idea 2] Of course, if we know the library function next_permutation of C ++, we don't have to worry about it because the Library FunctionAlgorithmThey are all encapsulated, so there is nothing to say, just go to the Code:

1 # Include <iostream>
 2 # Include < String >
 3   Using   Namespace STD;
 4  
 5   Void Stringpermutation ( Char * STR, Char * Perbegin)
 6 {
7       If (STR = NULL | perbegin = NULL)
 8           Return ;
 9  
 10       //  If the start position is the ending character, print all characters before the ending character  
  11       If (* Perbegin = '  \ 0  ' )
12 {
 13 Cout <STR <Endl;
 14 }
 15       Else 
 16 {
 17      
 18           For ( Char * PCH = perbegin; * PCH! = '  \ 0  ' ; ++ PCH)
 19 {
 20               //  Place where the nth character and the first character are exchanged  
  21               Char Temp = * PCH;
 22 * PCH = * perbegin;
 23 * Perbegin = temp;
 24  
 25               //  Sort all characters after the first character 
  26 Stringpermutation (STR, perbegin + 1 );
 27  
 28               //  Exchange the nth character with the first character  
  29 Temp = * PCH;
 30 * PCH = * perbegin;
 31 * Perbegin = temp;
 32 }
33 }
 34 }
 35  
 36   Void Stringpermutation ( Char * String )
 37 {
 38 Stringpermutation ( String , String );
 39 }
40  
 41   Int Main ()
 42 {
 43       Char P [] = "  ABC  " ;
 44  
 45 Stringpermutation (P );
 46      
 47       Return  0 ;
 48 }

The running result is as follows:

 

References:

[1] He Haitao blog: http://zhedahht.blog.163.com/blog/static/254111742007499363479/

[2] Full arrangement of standard library: http://hi.baidu.com/%D6%D5%BD%E1%D5%DF192/blog/item/a8ce8d23753d1eb64723e800.html

Note:

1) Compile all the code environments in this blogWin7 + vc6. All code has been debugged by the blogger.

2) BloggerPython27This blogArticleCopyright. For Network reprinting, please indicate the sourceHttp://www.cnblogs.com/python27/. You have any suggestions for solving the problem. Please feel free to comment on them.