3. Longest Substring Without Repeating Characters

Medium
Hash Table String Sliding Window

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

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3. Note that "bca" and "cab" are also correct answers.

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.

Constraints:

  • 0 <= s.length <= 5 * 10^4
  • s consists of English letters, digits, symbols and spaces.
func lengthOfLongestSubstring(s string) int {
	l := 0
	r := 1

	var canAdd = func(l, r int) bool {
		// fmt.Println("[ ] canAdd", l, r)
		sub := s[l:r]

		counts := map[rune]int{}
		for _, c := range sub {
			if counts[c] > 0 {
				// fmt.Println("[-] canAdd", sub)
				return false
			}
			counts[c]++
		}

		// fmt.Println("[+] canAdd", sub)
		return true
	}
	result := 0

	for l < len(s) {
		for r <= len(s) && canAdd(l, r) {
			result = max(result, r-l)
			r++
		}
		l++
	}

	return result
}
💡 Hints (1)
Hint 1
Generate all possible substrings & check for each substring if it's valid and keep updating maxLen accordingly.