Longest Substring Without Repeating Characters

#include <string>
#include <stack>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;
int lengthOfLongestSubstring(string s) {
vector<int> temp(256, -1);
int max_l = 0;
int begin = 0;
for (int i = 0; i < s.size(); i++) {
begin = max(temp[s[i]]+1, begin);
temp[s[i]] = i;
max_l = max(max_l, i - begin + 1);
}
return max_l;
}
int main() {
string b = "aabc";
string a = "0";
int res=lengthOfLongestSubstring(b);
}