Permutations Code

import java.util.ArrayList;

import java.util.List;

/**

 * // Pseudocode 

 * // Rule1: Return that permutation alone. 

 * // Rule2: ab >1 try to pick the last element seperately 

 * // and rest of the elements seperately lastelement, rest 

 * // Recursively // Position last element at all the possible

 * places. // merge the last element

 *

 */

public class Permutations {

static List<String> merge(List<String> list, String ch) {

List<String> mergedResult = new ArrayList<String>();

for (String element : list) {

// ab ch = 'c'

for (int i = 0; i <= element.length(); i++) { // ab c

String ps = new StringBuffer(element).insert(i, ch).toString();

mergedResult.add(ps);

}

}

return mergedResult;

}

// a

static List<String> permutation(String input) {

List<String> result = new ArrayList<String>();

// Rule1

if (input.length() == 1) {

result.add(input);

} else if (input.length() > 1) {

// Rule 2

int lastIndex = input.length() - 1;

// ab c

String last = input.substring(lastIndex);// c

String rest = input.substring(0, lastIndex);// ab

result = merge(permutation(rest), last);

}

return result;

}

public static void main(String[] args) {

System.out.println(permutation("abc"));

}

}