Longest Substring Without Repeating Characters

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

Example 1:

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

Example 2:

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

Example 3:

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

Example 4:

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Input: s = ""
Output: 0

Constraints:

0 <= s.length <= 5 * 104
s consists of English letters, digits, symbols and spaces.

Solution:

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class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        var set = new HashSet<Character>();
        int i = 0;
        int j = 0;
        int ans = 0;
        while (i < n && j < n) {
            // try to extend the range [i, j]
            if (!set.contains(s.charAt(j))) {
                set.add(s.charAt(j));
                j++;
                ans = Math.max(ans, j - i);
            } else {
                set.remove(s.charAt(i)); // important to remove first
                i++;
            }
       }
       return ans;
    }
}