# GeetCode Hub

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.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
```

Example 4:

```Input: s = ""
Output: 0
```

Constraints:

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

class Solution: def lengthOfLongestSubstring(self, s: str) -> int: slow = 0 fast = 0 max_len = 0 if len(s) <2: return len(s) dic = {} for k, t in enumerate(s): if t not in dic or slow > dic[t]: dic[t] = k fast += 1 max_len = max(max_len, fast-slow) else: slow = dic[t] + 1 dic[t] = k fast +=1 max_len = max(max_len, fast-slow) return max_len

The basic idea of solving this problem is to keep track of all the characters we have already visited and maintain a window size in which each character appeared only once. So throughout the traversal whenever the window size is maximum, that will give us the result.

Time Complexity: O(n)  // For traversing all the items in the array.

Space Complexity: O(n) // for keeping track of already visited items in the window, in the worst case all items will be present in the HashSet.

Medium