class Solution {
    public int longestSubstringWithoutDuplication(String s) {
            int freq[]=new int[128];
            int i=0,j=0,res=0;
            while(j<s.length()) {
                char c1=s.charAt(j);
                freq[c1]++;
                j++;
                while(freq[c1]>1){
                    char c2=s.charAt(i);
                    freq[c2]--;
                    i++;
                }
                res=Math.max(res,j-i);
            }
            return res;
    }
}