Huawei Machine Test ACM (character combination problem)

This evening did the Huawei's machine test, 3 ACM problem, the last is to achieve from the M different characters in any combination of n characters.

Eg:input:ABC 2

Output:ab AC BC

The first input is a string, the second input is the number of characters combined, and "error" is output when n=0 or n>m.

Idea: You can use recursive algorithm to solve, for example, all combinations of 2 characters in ABC, first select a, that contains a 2 characters of all combinations is to take 1 characters from the remaining BC in all combinations, and then select the second B, All combinations of the 2 characters that contain B are the combination of 1 characters from the remaining C in the back, that is, only C, when the third C is selected, there are no characters behind, and it is not enough to compose a 2-character combination. And so on, all combinations of n characters from any of the M different characters are recursively recursive to all combinations of N-1 characters (containing "a") from M-1, plus all combinations of n characters (not "a") that are selected from each of the M-1 characters.

Import java.util.*;p Ublic class Main {public static void main (String args[]) {        Scanner cin = new Scanner (system.in); 
   string str = Cin.next ();        int maxCount = Cin.nextint ();        char[] CHS = Str.tochararray ();        if (maxcount==0 | | Maxcount>str.length ()) {        System.out.print ("ERROR");        }        Combination (CHS, 0, 0, MaxCount, "");    }      /        * * @param CHS input character Array       * @param the array index value of the character selected by index *       @param count has selected the number of characters       * @param maxCount input to select  Number of characters       * @param result already selected character combination       * *   /public static void combination (char[] CHS, int index, int count, int MaxCount, String result) {   if (count = = MaxCount) {   System.out.print (result+ "");   return;   }   for (int i = index; i < chs.length; ++i) {   combination (CHS, i + 1, Count + 1, maxCount, result + chs[i]);   }   }}

　　

Huawei Machine Test ACM (character combination problem)