Find the longest substring without repeating characters.

Our solution processes the input string by iterating through it while maintaining a set of characters (char_set) that tracks the unique characters in the current window (substring without repeating characters). We use two pointers (left and right) to define the boundaries of this sliding window.

1. For each character s[right] in the string, we check whether it is already present in char_set.
2. If the character is already present, we remove characters from the left side of the window (i.e., we increment the left pointer) until the repeating character is removed from char_set.
3. After ensuring there are no repeating characters in the current window, we add s[right] to char_set.
4. We then update the maximum length of the substring found so far by comparing the current window size (right - left + 1) with the previous maximum length.

By maintaining a sliding window that expands and contracts dynamically as we move through the string, we can efficiently determine the length of the longest substring without repeating characters.

Time Complexity:
The time complexity of this solution is O(n), where n is the length of the string. Each character in the string is added to and removed from the char_set at most once, resulting in a linear pass through the string.

Space Complexity:
The space complexity is O(min(n, m)), where n is the length of the string and m is the size of the character set (i.e., 128 for ASCII or 256 for extended ASCII). This is because, in the worst case, we may need to store up to m unique characters in the set.