Java program to check if a string has unique characters without using additional space

This post is about a java program to check whether a string has unique characters without using additional memory space. The program is implemented with the help of bit vector.

The program is as follows:

package com.programs;

/*
 * Program to check if the string contains duplicate characters in an efficient way.
 */

public class strdups {

 public static void main(String args[])

 {

  String textWithDuplicateCharacters = "aabbcdefghij";
  String textWithUniqueCharacters = "abcdefghijklmnopqrstuvwxyz";

  printOutput(isUnique(textWithDuplicateCharacters));
  printOutput(isUniqueEfficient(textWithDuplicateCharacters));

  System.out.println();

  printOutput(isUnique(textWithUniqueCharacters));
  printOutput(isUniqueEfficient(textWithUniqueCharacters));

 }

 public static boolean isUnique(String str)

 {

  boolean[] char_set = new boolean[256];

  for (int i = 0; i < str.length(); i++)

  {

   int val = str.charAt(i);

   if (char_set[val])

   {

    return false;

   }

   char_set[val] = true;

  }

  return true;

 }

 // Efficient program without additional memory space

 public static boolean isUniqueEfficient(String str)

 {

  int check = 0;

  for (int i = 0; i < str.length(); i++)

  {

   int val = str.charAt(i) - 'a';

   if ((check & (1 << val)) > 0)

   {

    return false;

   }

   check |= (1 << val);

  }

  return true;

 }

 public static void printOutput(boolean bool) {
  if (bool == false)

  {

   System.out.println(" There are duplicate characters in the string");

  }

  else

  {

   System.out.println(" The string contains only unique characters");

  }

 }

}

The output for this program is as follows:

 There are duplicate characters in the string
 There are duplicate characters in the string

 The string contains only unique characters
 The string contains only unique characters

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Please comment below if you have any questions.