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# LeetCode 3. Longest Substring Without Repeating Characters

Two Pointer

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 * 10^4`
* `s` consists of English letters, digits, symbols and spaces.

## Solution:

[English Version in Youtube](https://youtu.be/51tTP5RJlQ0)

[中文版解答Youtube Link](https://youtu.be/BUXpASogwZw)

[中文版解答Bilibili Link](https://www.bilibili.com/video/BV17A411g7xk/)

```
class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        bool visited[256] = {false};
        int result = 0;
        int i = 0;
        
        for (int j = 0; j < s.length(); j++) {
            char ch = s[j];
            if (visited[ch] == false) {
                visited[ch] = true;
                result = max(result, j - i + 1);
            } else {
                while (s[i] != ch) {
                    visited[s[i]] = false;
                    i++;
                }
                i++;
            }
        }
        
        return result;
    }
};
```