gistfile1.txt

int Solution::lengthOfLongestSubstring(string A) {
    size_t longest = 0;
    // holds the characters of the current substring
    unordered_set<char> currSet;
    for (int i = 0; i < A.size(); ++i) {
        // if the current character already exists in the substring
        if (!currSet.insert(A[i]).second) {
            longest = max(longest, currSet.size());
            // erase the most senior elements of the set until insertion succeeds
            while (!currSet.insert(A[i]).second) {
                currSet.erase(A[i - currSet.size()]);
            }
        }
    }
    return max(longest, currSet.size());
}