1 class Solution { 2 public: 3     int lengthOfLongestSubstring(string s) { 4         const int ASCII_MAX = 256; 5         int last[ASCII_MAX]; 6         memset(last, -1, sizeof(last)); 7         int startPos = 0; int len = 0; 8         for (int i = 0; i < s.size(); ++i) { 9             if (last[s[i]] >= startPos) {10                 len = max(len, i - startPos);11                 startPos = last[s[i]] + 1;12             }13             last[s[i]] = i;14         }15         return max(len, static_cast<int>(s.size()) - startPos);16     }17 };