3. longest substring without repeating characters

#include <map>

class Solution {
public:
	int lengthOfLongestSubstring(std::string s) {
		std::map<char, int> flag;
		unsigned result = 0;
		unsigned j = 0;
		unsigned i = 0;
		while (j < s.length()) {
			for ( ; i < s.length(); ++i) {
				if (flag[s[i]] == 0) {
					flag[s[i]]++;
				} else {
					break;
				}
			}
			if (result < i - j) {
				result = i - j;
			}
			flag[s[j]]--;
			j++;
		}
		return result;
	}
};