Longest substring without repeating characters

This problem can be solved in O(n^2) time and O(n) space with the help of a hash.

The idea is to use two nested loops and check for every substring.

Use a HashSet to identify if the current substring has a repeating character.

The time complexity of this solution is O(n^2) and the space complexity is O(n).

This problem can be solved in O(n) time and O(n) space with the help of a sliding window.

The idea is to maintain a sliding window from the i^th to the j^th index.

Use a HashMap to identify if the current window has a repeating character. This map contains a character as a key and the character's index in the array as a value.

If a repeating character is found at the j^th index, look up the index of an already existing duplicate character in the map and move i to the next of this index.

While checking for repeating characters in a map, make sure that the repeating character is in the current window (at >=i^th index).

Keep incrementing the j^th index until it is less than or equals the last index and the character at the j^th index is not repeating.

In each iteration, if the length of the sliding window, i.e., "lengthTillHere," is greater than "lengthSoFar," update lengthSoFar = lengthTillHere.

The time complexity of this solution is O(n) and space complexity is O(n).