Java Challenge - Unique Characters in a String

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1

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This community-built FAQ covers the “Unique Characters in a String” code challenge in Java. You can find that challenge here, or pick any challenge you like from our list.

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2 
import java.util.*;

public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters(""));
  }

  public static boolean uniqueCharacters(String strIn) {
    if (strIn.length() == 0) {
      System.out.println("Error");
      return true;
    }
    ArrayList<String> list = new ArrayList<String>();
    for (int i = 0; i < strIn.length(); i++) {
      if (list.contains("" + strIn.charAt(i))) {
        return false;
      }
      list.add("" + strIn.charAt(i));
    }
    return true;
  }
}

This is what I keep trying as my solution, but it doesn’t work for some reason. I keep getting 4/5 tests correct. I suspect it has something to do with this part of the questions: “Note that if the function is called with an empty string (”“), the program should return an error message.” I’m not really sure how to deal with this as you can’t throw an exception of the tester will break, printing a string isn’t enough, and you can’t change the return type from boolean without the tester breaking. Anyone have an answer?

3

I pass same 4/5. Not sure where the problem is.

import java.util.*;

public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters("apple"));
  }

  public static boolean uniqueCharacters(String strIn) {
        if(strIn == null || strIn.isEmpty()){
            System.out.println("Bad string");
            return false;
        }
        for (int i = 0; i < strIn.length() - 1; i++) {
            for (int j = i + 1; j < strIn.length(); j++) {
                if (strIn.charAt(i) == strIn.charAt(j)) {
                    return false;
                }
            }
        }
        return true;
    }

}
4

To pass all tests program should not return a boolean along with the error message if the inputted string is blank.


import java.util.*;
public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters(""));
  }
  public static boolean uniqueCharacters(String strIn) {
  if (strIn == "")
  {
    System.out.println("Error"); 
    System.exit(0); // if string is blank, return error and end program
  }
    char[] strToArray = strIn.toCharArray(); // convert string to char array
    Arrays.sort(strToArray); // sort array alphabetically
    boolean result = true; // declare boolean result variable and set to true.
    // loop through array - compare index i with index i + 1 - bool set to false if they match
    for(int i = 0; i < strToArray.length - 1; i++)
    {
      if (strToArray[i] == strToArray[i+1])
      {
        result = false; 
      }        
    }
    return result;
  }
}
4 Likes
5

Thank you so much, this works

2 Likes
6 
import java.util.*;

public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters("apple"));
  }

  public static boolean uniqueCharacters(String strIn) {
    if (strIn.isEmpty()){
      return false;
    }
    for (int i = 0; i < strIn.length() - 1; i++) {
      for (int j = i + 1; j < strIn.length(); j++) {
        if (strIn.charAt(i) == strIn.charAt(j)) {
          return false;
        }
      }
    }
    return true;
  }

}
7

This is how I solved this challenge:

import java.util.*;

public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters("apple"));
   
  }//end main

  public static boolean uniqueCharacters(String strIn) {
    if(strIn.isEmpty())
    {
      return false;
    }
    
     for(int i=0;i<strIn.length();i++)
    {
      //check for repeated chart i from i+1 to end of string
     if( i!= strIn.length()-1 && strIn.indexOf(strIn.charAt(i),i+1) != -1)
      return false;
    }
    return true;
  }//end method uniqueCharacters

}//end class
8

My simple java solution!!

import java.util.*;

public class UniqueCharacters {
  public static void main(String[] args) {
    System.out.println(uniqueCharacters("apple"));
  }

  public static boolean uniqueCharacters(String strIn) {

    char[] str = strIn.toCharArray();

    if(str.length==0)
    {
      return false;
    }
    else
    {
      for(int i = 0; i<str.length; i++)
      {
        for(int j = i+1; j<str.length; j++)
        {
          if(str[i]==str[j])
          {
            return false;
          }
        }
      }
    }
    return true;
    
  }

}
9

import java.util.*;

public class UniqueCharacters {
public static void main(String args) {
System.out.println(uniqueCharacters(“apple”));
}

public static boolean uniqueCharacters(String strIn) {

    if (strIn.isEmpty()){
        return  false ;
    }

    Set<Character> wordSet = new HashSet<>();
    for (char c :strIn.toCharArray() ){
        wordSet.add(c);
    }

    return  strIn.toCharArray().length == wordSet.size();

}

}