Remove duplicates from a string

Method-3: Using Hashing
In this case we will use a separate array (which will act as hash table) to store the number of occurrences of a character in the string.

Step-1: Populate the hash (array) to store the number of times a character appears in the array.
        If original string is "social.ritambhara.in", then the hash array will have
    arr['s'] = 1
    arr['o'] = 1
    arr['c'] = 1
    arr['i'] = 3
    arr['a'] = 4
    arr['l'] = 1
    arr['.'] = 2
    arr['r'] = 2
    arr['t'] = 1
    arr['m'] = 1
    arr['b'] = 1
    arr['h'] = 1
Step-2: Now traverse the array from backward direction and for each character
   - remove the character if its hash count is > 1.
   - Decrease the corresponding hash count.

Code:

    void removeDuplicatesUsingHash(char* str)
    {
        int hash[256] = {0};
        // Populating the hash.
        for(int i=0; str[i] != '\0'; i++)
            hash[str[i]]++;
        // traversing the array from back and
        // removing the characters if its hash value is > 1
        for(int i = strlen(str)-1; i>0; i--)
        {
            // Need to do this here, because str[i] may change in loop below.
            hash[str[i]]--;
            if(hash[str[i]] > 0)
            {
                // Removing the character.
                int j=i;
                for(; str[j] != '\0'; j++)
                    str[j] = str[j+1];
            }
        }
    }

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