Longest Substring Without Repeating Characters — C++

// Time:  O(n)
// Space: O(1)

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int result = 0;
        unordered_map<char, int> lookup;
        for (int left = 0, right = 0; right < s.length(); ++right) {
            if (lookup.count(s[right])) {
                left = max(left, lookup[s[right]] + 1);
            }
            lookup[s[right]] = right;
            result = max(result, right - left + 1);
        }
        return result;
    }
};