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Leetcode 3 Longest Substring Without Repeating Characters - Medium

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3. Longest Substring Without Repeating Characters - Medium

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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 = "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 3: 
Input: s = ""
Output: 0
Solution: Two Pointers - Sliding Window, Hash Set for detecting duplicates, Space O(N), Time O(N) 
class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        longest = 0
        visited = set()
        j = 0
        for i in range(len(s)):
            while j < len(s) and s[j] not in visited:
                visited.add(s[j])
                j += 1
                longest = max(longest, j - i)
            # sliding the window, 
            # by removing the i ptr element in visited
            visited.remove(s[i])
            # prunning
            if j >= len(s):
                break
        return longest

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