Backtracking 2 - Generate all combinations of String characters for n digits.

"For a given String of n characters length, generate all combinations for k digits"

Using recursive procedure, we can generate all possible combinations.

Input :

• String of length n will be given
• k - digits for which the combinations need to be generated.

For Eg, if String s = "ab", the combinations are "aa, ab, bb, ba"

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public class StringPermutationUsingRecursion{ public static void main(String args[]){ String s = "ab"; int k = 3; StringPermutationUsingRecursion permutation = new StringPermutationUsingRecursion(); permutation.printAllString(s,"", k); } public void printAllString(String s,String suffix, int k){ if(k <1 ){ System.out.println(suffix); return; } else { for(int i = 0; i < s.length();i++){ String newsuffix = suffix+s.charAt(i); printAllString(s,newsuffix, k-1); } } } }

 The algorithm goes as below,

1. Iterate over given string, form a substring 
2. Recursively call the function until the k is less than 1.
3. Print the substring when k reaches 0 or less than 1.

The order or sequence which we generate manually may change.