length of longest unique substring

longest_unique_substring_sliding_window.py

from collections import defaultdict

def longest_unique_substring(s):
    longest_length = float('-inf')
    n = len(s)

    # empty string has the longest length is 0
    if n == 0:
        return 0

    left = 0
    right = 0
    window = defaultdict(int)
    while right < n:
        # sliding the window to the right
        right_character = s[right]
        window[right_character] += 1
        right += 1

        # if a duplicate character appears in the window
        # drop off the left elements until we have valid condition again
        while window[right_character] > 1:
            window[s[left]] -= 1
            left += 1
        longest_length = max(longest_length, right - left)

    return longest_length