# Leetcode 筆記 :(3) Longest Substring Without Repeating Characters

###### tags: `Leetcode`

## 題目
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

## 嘗試

1. while 後面接上 else ，這在迴圈條件為假的時候執行。
2. 使用Sliding Window

## Code

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        sub_str = ''
        max_len = 0
        
        for i in s:
            while i in sub_str:
                sub_str = sub_str[1:]
            else:
                sub_str += i
                max_len = max(len(sub_str), max_len)
        
        return max_len

PTT 上找到的解答

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        indices, j, ans = {}, 0, 0
        for i, c in enumerate(s):
            if c in indices:
                j = max(indices[c] + 1, j)
            ans = max(ans, i - j + 1)
            indices[c] = i
        return ans