3. Longest Substring Without Repeating Characters

#include <algorithm>class Solution {public:    int lengthOfLongestSubstring(string s) {        set<char> mapping;        int best = 0;        int l = 0;        for (int r = 0; r < s.size(); r++) {            // not adding s[r] yet because we need to clean up the set for            // s[r] to join            while (mapping.find(s[r]) != mapping.end()) {                // if this is the case, there is a duplicate in the                // substring somewhere                mapping.erase(s[l]);                l++;            }            mapping.insert(s[r]);  // now safe to add s[r]            // after all dups are removed, we found a valid substring that            // meets the condition, lets check with best            best = max(best, r - l + 1);        }        return best;    }};