The problem belongs to LeetCode, here is the link to the problem

Following code segment contains the description in the class comments, followed by fully working solution

/**
 * Given a string s, find the length of the longest substring without repeating characters.

 * Example 1:
 * Input: s = "abcabcbb"
 * Output: 3
 * Explanation: The answer is "abc" with the length of 3.
 * 
 */
public class LongestSubstring {
    // this method is provided by leetcode , adding dummy logic here.
    public int lengthOfLongestSubstring(String s) {
        if(s==null || s.length()<=0) return 0;
        char[] arr=s.toCharArray();
        int mlen=1;
        int st=0;
        int len=0;
        int[] map = new int[256];

        Arrays.fill(map, -1);
        for(int i=0;imlen){
                    mlen=len;
                }
            }else{
                // arr[i] already exists
                int k = map[arr[i]];
                for(int p=st;p<=k;p++){
                    map[arr[p]] = 0;
                    len--;
                }
                st=k+1;
                map[arr[i]] = i;
                len++;
            }
        }
        return mlen;
    }
}