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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4. import java.util.stream.*;
  5. import java.util.stream.Collectors; 
  6.  
  7. class Ideone
  8. {
  9. 	public static void main (String[] args) throws java.lang.Exception
  10. 	{
  11. 		String a = "ABC"; 
  12.  
  13.         StringBuilder b = new StringBuilder(); 
  14.  
  15.         List<String> combinations = new ArrayList<>();
  16.  
  17.         combine(a, b, 0, 0, combinations);
  18.  
  19.         List<String> filtered = combinations.stream()
  20.  
  21.                                                   .filter(t -> t.length() == 2)
  22.  
  23.                                                   .collect(Collectors.toList());
  24.  
  25.  
  26.         filtered.stream()
  27.  
  28.                 .forEach(t -> {
  29.  
  30.                 	        List<String> permutations = new ArrayList<>();
  31.  
  32.                 	        StringBuilder sb = new StringBuilder();
  33.  
  34. 					        boolean used[] = new boolean[2]; 
  35.  
  36. 					        used[0] = false; 
  37.  
  38. 					        used[1] = false; 
  39.  
  40. 					        permute(t, sb, used, permutations); 
  41.  
  42. 					        for(String s: permutations){ 
  43.  
  44. 					            System.out.println(s); 
  45.  
  46. 					        } 
  47.  
  48.                 });
  49.  
  50. 	}
  51.  
  52. 	public static void combine(String a, StringBuilder b, int start, int level, List<String> combinations) { 
  53.  
  54.      for (int i = start; i < a.length(); i++) { 
  55.  
  56.         if (b.toString().contains(String.valueOf(a.charAt(i))) == false) { 
  57.  
  58.             b.append(a.charAt(i)); 
  59.  
  60.             combinations.add(b.toString()); 
  61.  
  62.             if (i < a.length() - 1) { 
  63.  
  64.                 combine(a, b, start + 1, level + 1, combinations); 
  65.  
  66.             } 
  67.  
  68.             b.setLength(b.length() - 1); 
  69.  
  70.         } 
  71.  
  72.      } 
  73.  
  74.   } 
  75.  
  76.     public static void permute(String a, StringBuilder b, boolean[] used, List<String> permutations) { 
  77.  
  78.         if ( b.length() == a.length()) { 
  79.  
  80.             permutations.add(b.toString()); 
  81.  
  82.             return; 
  83.         } 
  84.  
  85.         for (int i  =  0; i < a.length(); i++) { 
  86.  
  87.             if (used[i]) {continue;} 
  88.  
  89.             used[i] = true; 
  90.  
  91.             b.append(a.charAt(i)); 
  92.  
  93.             permute(a, b, used, permutations); 
  94.  
  95.             b.setLength(b.length()-1); 
  96.  
  97.             used[i] = false; 
  98.  
  99.         }  
  100.  
  101.     } 
  102.  
  103. } 
  104.  
Success #stdin #stdout 0.08s 34248KB
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Standard input is empty
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AB
BA
AC
CA
BC
CB
https://ideone.com/DBjnkH
language:
Java (HotSpot 12)
created:
3 years ago
visibility:
public

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