Given a string, input_str, return the length of the longest substring without repeating characters.

Constraints:

• $1$ $\leq$ input_str.length $\leq 10^5$
• input_str consists of English letters, digits, symbols, and spaces.

So far, you’ve probably brainstormed some approaches on how to solve this problem. Let’s explore some of these approaches and figure out which one to follow while considering time complexity and any implementation constraints.

The naive approach is to explore all possible substrings. For each substring, we check whether any character in it is repeated. After checking all the possible substrings, the substring with the longest length that satisfies the specified condition is returned.

The total time complexity of this solution is $O(n^3)$ ...