LeetCode03题，无重复字符最长子串

int lengthOfLongestSubstring(string s) {
	if (s.size() == 0) return 0;
	unordered_set<char> lookup;
	int maxStr = 0;
	int left = 0;
	for (int i = 0; i < s.size(); i++) {
		while (lookup.find(s[i]) != lookup.end()) {
			lookup.erase(s[left]);
			left++;
		}
		maxStr = max(maxStr, i - left + 1);
		lookup.insert(s[i]);
	}
	return maxStr;
}