3_longest_substring_without_repeating_chars.cpp

/*
LeetCode 3 - Longest Substring Without Repeating Characters
Difficulty: Medium

Problem:
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

Example 3:
    Input: s = "pwwkew"
    Output: 3

Constraints:
    0 <= s.length <= 5 * 10^4
    s consists of English letters, digits, symbols and spaces.

Time Complexity: O(n)
Space Complexity: O(min(m, n)) where m is the size of the charset
*/

#include <iostream>
#include <string>
#include <unordered_map>
#include <algorithm>

using namespace std;

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_map<char, int> char_index;
        int left = 0;
        int max_len = 0;

        for (int right = 0; right < s.length(); right++) {
            char c = s[right];
            if (char_index.find(c) != char_index.end() && char_index[c] >= left) {
                left = char_index[c] + 1;
            }
            char_index[c] = right;
            max_len = max(max_len, right - left + 1);
        }

        return max_len;
    }
};

int main() {
    Solution solution;

    cout << solution.lengthOfLongestSubstring("abcabcbb") << endl;  // 3
    cout << solution.lengthOfLongestSubstring("bbbbb") << endl;     // 1
    cout << solution.lengthOfLongestSubstring("pwwkew") << endl;    // 3
    cout << solution.lengthOfLongestSubstring("") << endl;          // 0

    return 0;
}