# Leetcode - Longest Substring Without Repeating Characters Solution

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.
```

**Constraints:**

`0 <= s.length <= 5 * 10`

^{4}`s`

consists of English letters, digits, symbols and spaces.

### Solution in Python3

```
class Solution:
def lengthOfLongestSubstring(self, s: str) -> int:
best = 0
non_unique = -1
seen = {}
for index,char in enumerate(s):
last_seen = seen.get(char, -1)
non_unique = max(non_unique, last_seen)
best = max(index-non_unique, best)
seen[char] = index
return best
```