Permutations.java

package com.lchau;

public class Permutations {

  public static void main(String[] args) {
    String str = "Hello, world";
    Permutations.permute(0, str.length() - 1, str.toCharArray());
  }

  private static boolean match(int i, int j, char[] chars) {
    if (i != j) {
      for (; i < j; i++) {
        if (chars[i] == chars[j]) {
          return true;
        }
      }
    }
    return false;
  }

  private static void permute(int index, int length, char[] str) {
    if (index == length) {
      System.out.println(new String(str));
      return;
    }

    for (int i = index; i <= length; i++) {
      if (Permutations.match(index, i, str)) {
        continue;
      }
      Permutations.swap(index, i, str);
      Permutations.permute(index + 1, length, str);
      Permutations.swap(index, i, str);
    }
  }

  private static void swap(int i, int j, char[] str) {
    char temp = str[i];
    str[i] = str[j];
    str[j] = temp;
  }

}