LeetCode Solution - Problem Longest Substring Without Repeating Characters

• 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.

Constraints:

• 0 <= s.length <= 5 * 104 
• s consists of English letters, digits, symbols, and spaces.

Solution:

Java:

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int ans = 0;
        HashMap<Character, Integer> map = new HashMap<>();
        int left = 0;
        for (int right=0; right < s.length(); right++) {
            char ch = s.charAt(right);
            if (!map.containsKey(ch)) {
                map.put(ch, right);
            }
            else {
                left = Math.max(left, map.get(ch) + 1);
                map.put(ch, right);
            }
            ans = Math.max(ans, right - left + 1);
        }
        return ans;
    }
}

Python:

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        char_set = set()
        max_len, start = 0, 0
        for i, c in enumerate(s):
            while c in char_set:
                char_set.remove(s[start])
                start += 1
            char_set.add(c)
            max_len = max(max_len, i - start + 1)
        return max_len