3. Longest Substring Without Repeating Characters

Medium LeetCode

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.

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.

Constraints:

• 0 <= s.length <= 5 * 10^4
• s consists of English letters, digits, symbols and spaces.

How to solve the problem

• Sliding Window

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        left = 0
        substring = set()
        result = 0
        for right in range(len(s)):
            while s[right] in substring:
                substring.remove(s[left])
                left += 1
            substring.add(s[right])
            length = right - left + 1
            result = max(length, result)
        return result

Complexity

• Time Complexity: O(n) - Each character is visited at most twice (once by right pointer, once by left pointer)
• Space Complexity: O(min(m, n)) - Where m is the size of the character set and n is the length of string. The set stores at most min(m, n) characters