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

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

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

Solution:

Sliding window.

If char of right pointer doesn’t exist in the set, add it and expand the window.

Else, remove it and shift the window.

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int left = 0;
        int right = 0;
        int max = 0;
        Set<Character> set = new HashSet<>();
        
        while (right < n) {
            if (!set.contains(s.charAt(right))) {
                set.add(s.charAt(right++));
                max = Math.max(max, right - left);
            } else {
                set.remove(s.charAt(left++));
            }
        }
        
        return max;
    }
}

Time complexity: O(n), the right pointer will only iterate n time.

Space complexity: O(n).