116-longest-substring-with-max-k-distinct-characters

public static Integer longestDistinctSubstring(String str, Integer k){ 
    //solution here
    Integer max = -1;
    Integer start =0;
    Map<Integer,Integer> freq = new Map<Integer,Integer>();

try{

    for(Integer i =0;i < str.length();i++)
    {
        Integer elm = str.charAt(i);
        Integer count =0;
        if(freq.get(elm) == null ) {
            k--;
            count++;
        }else {
            count = freq.get(elm) +1;
        }
        freq.put(elm,count);
        while(k < 0 )
        {
            elm = str.charAt(start);
            count = freq.get(start)-1;
            start++;
            freq.put(elm, count);
            if(count == 0)k++;
        }
        max = Math.max(max, i-start+1);
    }
}catch(Exception ex)
{
    system.debug(ex.getMessage());
}
    return max;

}