CODEWITHSUNDEEP
javastringhashtable
fscore
fscore

Reputation: 2619

Find if a string is unique or not

I want to use hashtable to find unique characters as it seems more efficient to me so for example, hello in hashtable would be=> {h:1,e:1,l:2,o:1} & since value is more than 1 then string isnt unique. I know I can do ascii way of counting unique characters but I want to implement the hashtable way.

Please note, I do not want a regex implementation.

static void findHashUnique(String str)
{
    Hashtable<Character, Integer> ht = new Hashtable<Character, Integer>();
    for(int i=0;i<str.length();i++)
    {
        int cnt=1;

        if(!ht.containsKey(str.charAt(i)))
        {
            ht.put(str.charAt(i), cnt);
        }
    }
    System.out.print(ht);
}

I am stuck at the part of how will I first initialize the hashtable & also check if value exists then increment. In case of 'l' it will increment to 2 instead of being 1 since the key is the same. Also Is this solution efficient?

Upvotes: 1

Views: 1271

Answers (3)

Tdorno
Tdorno

Reputation: 1571

Here's my approach.

String string = "hello";
Hashtable<Character, Integer> map = new Hashtable<>();
for (int i = 0; i < string.length(); i++) {
   char c = string.charAt(i);
   if (map.containsKey(c)) {
      map.put(c, map.get(c) + 1);
   } else {
      map.put(c, 1);
   }
}
System.out.println(map);

Output: {e=1, o=1, l=2, h=1}

Upvotes: 2

Hunter McMillen
Hunter McMillen

Reputation: 61512

Well, I don't know exactly what character encodings you will be examining, but if you are constraining yourself to only ASCII characters, you can use a simple array of 128 elements. 

public static String uniqueLetters(String s) {
   // storage for ascii characters
   char[] letters = new char[128];

   // mark counts of all letters
   for(int i = 0; i < s.length(); i++) {
      letters[ (int)s.charAt(i) ]++;
   }

   // find unique letters
   String uniques = "";
   for(int i = 0; i < letters.length; i++) {
      if ( letters[i] == 1 ) {
         uniques += Character.toString( (char)letters[i] );
      }
   }

   return uniques;
}

Upvotes: 2

Bohemian
Bohemian

Reputation: 424983

To "fix" your code, use a HashSet<Character>, which uses a Hashtable internally, but you don't have to know or worry about that. Just keep adding the chars to the set and you'll be left with a unique set of chars at the end.

To achieve the intention more easily:

String uniqueChars = str.replaceAll("(.)(?=.*\\1)", "");

Upvotes: 0

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