Add permutations of a string (fixes #2680) (#2682)

Strings/PermuteString.java

@@ -0,0 +1,50 @@
+/*
+Backtracking algorithm used in the program:-
+
+>>Fix a character in the first position and swap the rest of the character with the first character.
+  Like in ABC, in the first iteration three strings are formed: ABC, BAC, and CBA by swapping A with
+  A, B and C respectively.
+>>Repeat step 1 for the rest of the characters like fixing second character B and so on.
+>>Now swap again to go back to the previous position. E.g., from ABC, we formed ABC by fixing B again,
+  and we backtrack to the previous position and swap B with C. So, now we got ABC and ACB.
+>>Repeat these steps for BAC and CBA, to get all the permutations.
+*/
+public class PermuteString {    
+    //Function for swapping the characters at position I with character at position j    
+    public static String swapString(String a, int i, int j) {    
+        char[] b =a.toCharArray();    
+        char ch;    
+        ch = b[i];    
+        b[i] = b[j];    
+        b[j] = ch;    
+        return String.valueOf(b);    
+    }    
+        
+    public static void main(String[] args)    
+    {    
+        String str = "ABC";    
+        int len = str.length();    
+        System.out.println("All the permutations of the string are: ");    
+        generatePermutation(str, 0, len);    
+    }    
+        
+    //Function for generating different permutations of the string    
+    public static void generatePermutation(String str, int start, int end)    
+    {    
+        //Prints the permutations    
+        if (start == end-1)    
+            System.out.println(str);    
+        else    
+        {    
+            for (int i = start; i < end; i++)    
+            {    
+                //Swapping the string by fixing a character    
+                str = swapString(str,start,i);    
+                //Recursively calling function generatePermutation() for rest of the characters     
+                generatePermutation(str,start+1,end);    
+                //Backtracking and swapping the characters again.    
+                str = swapString(str,start,i);    
+            }    
+        }    
+    }    
+}