# Longest Substring Without Repeating Characters

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 * 104
- s consists of English letters, digits, symbols and spaces.

## Solution

### Another Sliding Window

This one makes perfect sense!

```
class Solution {
public int lengthOfLongestSubstring(String s) {
var max = 0;
var freq = new int[128];
var l = 0;
var r = 0;
while (r < s.length()) {
var c = s.charAt(r);
freq[c] += 1;
while (freq[c] > 1) {
var c2 = s.charAt(l);
freq[c2] -= 1;
l += 1;
}
max = Math.max(max, r - l + 1);
r += 1;
}
return max;
}
}
```

### Sliding Window

I donâ€™t really understand this one.

```
class Solution {
public int lengthOfLongestSubstring(String s) {
var l = 0;
var m = new HashMap<Character, Integer>();
var answer = 0;
for (var r = 0; r < s.length(); r++) {
var c = s.charAt(r);
if (m.containsKey(c)) {
l = Math.max(m.get(c), l);
}
m.put(c, r + 1);
answer = Math.max(r - l + 1, answer);
}
return answer;
}
}
```

### Another Unoptimized

```
class Solution {
public int lengthOfLongestSubstring(String s) {
// brute force
var max = 0;
for (var l = 0; l < s.length(); l++) {
for (var r = l; r < s.length(); r++) {
var freq = new boolean[128];
var ok = true;
// check if this string is valid
for (var i = l; i <= r; i++) {
var c = (int) s.charAt(i);
if (freq[c]) {
ok = false;
break;
}
freq[c] = true;
}
if (ok) {
max = Math.max(max, r - l + 1);
}
}
}
return max;
}
}
```

### Unoptimized

I think this solution is correct, but it hits a time limit exceeded error

```
class Solution {
public int lengthOfLongestSubstring(String s) {
var size = s.length();
while (size > 0) {
for (var l = 0; l <= s.length() - size; l++) {
var r = l + size;
// check if any of the letters in this range are duplicated
var set = new HashSet<Character>();
var ok = true;
for (var c : s.substring(l, r).toCharArray()) {
if (set.contains(c)) {
ok = false;
break;
} else {
set.add(c);
}
}
if (ok) {
return size;
}
}
size -= 1;
}
return size;
}
}
```