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.

```
class Solution {
public:
int lengthOfLongestSubstring(string str) {
int n = str.size();
int res = 0;
for (int i = 0; i < n; i++) {
vector<bool> visited(256);
for (int j = i; j < n; j++) {
if (visited[str[j]] == true)
break;
else {
res = max(res, j - i + 1);
visited[str[j]] = true;
}
}
visited[str[i]] = false;
}
return res;
}
};
```