length of longest unique substring

longest_unique_substring_brute_force.py

def longest_unique_substring(s):
    # function to check if the characters in the substring are all unique or not
    def is_all_unique(start_index, end_index):
        character_set = set()
        for z in range(start_index, end_index):
            if s[z] in character_set:
                return False
            character_set.add(s[z])
        return True

    longest_length = float('-inf')
    n = len(s)

    # empty string has 0 substring
    if n == 0:
        return 0

    # enumerate all substrings [i, j)
    for i in range(n):
        for j in range(i + 1, n + 1):
            # if the characters in the substring are all unique, compare the length.
            if is_all_unique(i, j):
                longest_length = max(longest_length, j - i)

    return longest_length