Leetcode•Jul 31, 2025
Longest Substring Without Repeating Characters
Hazrat Ali
Leetcode
Given a string s, find the length of the longest without duplicate characters.
Example 1:
Input: s = "abcabcbb" Output: 3 Explanation: The answer is "abc", with the length of 3.
Example 2:
Input: s = "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1.
Example 3:
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.
Solution
/**
* @param {string} s
* @return {number}
*/
const lengthOfLongestSubstring = s => {
const set = new Set();
let max = 0;
for (let i = 0, j = 0; j < s.length; j++) {
while (set.has(s[j])) {
set.delete(s[i]);
i++;
}
set.add(s[j]);
max = Math.max(max, set.size);
}
return max;
};