Longest Substring Without Repeating Characters

Tested Python solution for LeetCode 3 with 13 pytest cases. Generate a practice environment with lcpy.

LeetCode 3, Medium. Topics: Hash Table, String, Sliding Window. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 13 parametrized pytest cases, and a playground notebook:

lcpy gen -n 3   # by problem number
lcpy gen -s longest_substring_without_repeating_characters   # by problem name

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Problem

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

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Examples

Input: s = "abcabcbb"
Output: 3

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

Input: s = "bbbbb"
Output: 1

Explanation: The answer is “b”, with the length of 1.

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.

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Constraints

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

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Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(n)
    # Space: O(min(m, n)) where m is charset size
    def length_of_longest_substring(self, s: str) -> int:
        seen: set[str] = set()
        left = max_len = 0

        for right in range(len(s)):
            while s[right] in seen:
                seen.remove(s[left])
                left += 1
            seen.add(s[right])
            max_len = max(max_len, right - left + 1)

        return max_len

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Complexity

Time	Space
O(n)	O(min(m, n)) where m is charset size

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Tags

Grind 75, Grind, Blind 75, NeetCode 150, NeetCode 250, NeetCode All, AlgoMaster 75.