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.

Solution:

```
class Solution {
public int lengthOfLongestSubstring(String s) {
Set<Character> set = new HashSet<Character>();
int i=0, j=0, ans=0;
while(j<s.length())
{
if(!set.contains(s.charAt(j)))
{
set.add(s.charAt(j));
j++;
ans=Math.max(ans,j-i);
}
else
{
set.remove(s.charAt(i));
i++;
}
}
return ans;
}
}
```

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