3. Longest Substring Without Repeating Characters

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

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
             Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

JAVA

class Solution_map {
    public int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }

        int result = 0;
        HashMap<Character, Integer> hm = new HashMap<>();

        for (int left = 0, right = 0; right < s.length(); right++) {
            char probeChar = s.charAt(right);
            if (hm.containsKey(probeChar)) {
                left = Math.max(left, hm.get(probeChar) + 1);
            }
            hm.put(probeChar, right);
            result = Math.max(result, right - left + 1);
        }

        return result;
    }
} 

C++

int 
lengthOfLongestSubstring(string s) {
    int ans = 0, start = -1;
    vector<int> m(128, -1); // assume ASCII character set
    for (int i = 0; i < s.size(); ++i) {
        start = max(start, m[s[i]]);
        m[s[i]] = i;
        ans = max(ans, i - start);
    }
    return ans;
}

PYTHON

var lengthOfLongestSubstring = function (s) {
    const ss = new Set();
    let i = 0;
    let ans = 0;
    for (let j = 0; j < s.length; ++j) {
        while (ss.has(s[j])) {
            ss.delete(s[i++]);
        }
        ss.add(s[j]);
        ans = Math.max(ans, j - i + 1);
    }
    return ans;
};