Another from the archives. In my old notes I tried a few different approaches. Ultimately this one feels a little “brute-force-y”, here is what I got:

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int res = 0;
        for (int i = 0; i < s.size(); i++) {
            for (int l = std::max(res, 1); l + i <= s.size(); l++) {
                std::bitset<256> seen;
                bool bad = false;
                for (int j = i; j < i + l; j++) {
                    if (seen.test(s[j])) {
                        bad = true;
                        break;
                    }
                    seen.set(s[j]);
                }
                if (!bad) {
                    res = std::max(res, l);
                } else {
                    // i i our starting point, a longer l won't help here.
                    break;
                }
            }
        }
        return res;
    }
};

Thoughts

1. The “length” iteration (how i, l, j indexes interact) is pretty interesting. Comes up rarely, but in thinking about many collections of substrings.
2. The final “break” (with the comment above it) is necessary.
3. I wanted to port this to Python—my old archives are in C++. But it lacks a bitset class, and its range loops aren’t amenable to the length-based iteration (or at least, I don’t know how to adapt them).

I doubt my solution is the right one. What is the official Leetcode solution? Oh I like it! Does this make the cut as an interview question? I don’t know, I am skeptical. More string questions here.