LeetCode-in-All

3. Longest Substring Without Repeating Characters

Medium

Given a string s, find the length of the longest substring without repeating characters.

Example 1:

Input: s = “abcabcbb”

Output: 3

Explanation: The answer is “abc”, with the length of 3.

Example 2:

Input: s = “bbbbb”

Output: 1

Explanation: The answer is “b”, with the length of 1.

Example 3:

Input: s = “pwwkew”

Output: 3

Explanation: The answer is “wke”, with the length of 3. Notice that the answer must be a substring, “pwke” is a subsequence and not a substring.

Example 4:

Input: s = “”

Output: 0

Constraints:

Solution

defmodule Solution do
  @spec length_of_longest_substring(s :: String.t()) :: integer
  def length_of_longest_substring(s) do
    sublen([], String.codepoints(s), 0, 0, 0)
  end

  defp sublen(_, [], _, _, m), do: m
  
  defp sublen(left, [next | rest] = right, start, stop, m) do
    if Enum.member?(left, next) do
      [_ | mid] = left
      sublen(mid, right, start + 1, stop, m)
    else
      stop = stop + 1
      sublen(left ++ [next], rest, start, stop, max(m, stop - start))
    end
  end
end