Write a program to print all permutations of a given string

PermuteString.java

import java.util.*;

class PermuteString {
  public static void main(String[] args) {
    String abc = "ABC";
    System.out.println(Solution.permutation(abc));
  }
}

class Solution {
  public static List<String> permutation (String str) {
    List<String> result = new ArrayList<>();
    permute(result, str, 0, str.length()-1);
    return result;
  }

  public static void permute(List<String> list, String str, int start, int end) {
    // System.out.println("hello");

    if (start == end) {
      list.add(new String(str));
    } else {

      for (int i = start; i <= end; i++) {

        //swap
        str = swap(str, start, i);

        //permute
        permute(list, str, start+1, end);

        //replace
        str = swap(str, start, i);

      }
    }
  }

  public static String swap(String str, int first, int second) {

    char[] arr = str.toCharArray();

    char temp = arr[second];
    arr[second] = arr[first];
    arr[first] = temp;

    return new String(arr);
  }

}