problem 3. Longest Substring Without Repeating Characters

 1 class Solution {
 2 public:
 3     int lengthOfLongestSubstring(string s) {
 4         vector<int> signs(256, -1);
 5         int max_length = 0;
 6         int last_valid = -1;
 7         for (size_t i = 0; i < s.size(); ++i){
 8             char c = s[i];
 9             int last_occ = signs[c];
10             if (last_occ < last_valid){
11                 last_occ = last_valid;
12             }
13             if (last_occ > last_valid){
14                 last_valid = last_occ;
15             }
16             int length = i - last_occ;
17             if (length > max_length){
18                   max_length = length;
19             }
20             
21             signs[c] = i;
22         }
23         if (max_length == 0){
24             max_length = s.size();
25         }
26         return max_length;
27     }
28 };