Longest Substring Without Repeating Characters

Question

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

Example 1:

Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, with the length of 3.

LeetCodeleetcode.com/problems/longest-substring-without-repeating-characters/solution

Solution

/*
@param: s input string;
@return: int, longest length of substring;
Algorithm: two pointers, hashset, check repeat in substring(i,j), if no repeat,j++, else i++;
follow up hashset could be replaced by char[256];
*/
public int lengthOfLongestSubstring(String s) {
    if (s.length() == 0) return 0;
    
    Set<Character> set = new HashSet<>();        
    int ans = Integer.MIN_VALUE;
    for (int i = 0, j = 0; i < s.length(); i++) {
        while (j < s.length()) {                
            if (!set.contains(s.charAt(j))) {
                set.add(s.charAt(j));
                j++;
                ans = Math.max(ans, j-i);
            }else break;                
        }    
        set.remove(s.charAt(i));
    }
    return ans;
}