Longest Substring Without Duplication

• Time : O(n)
• Space : O(1)

using namespace std;

string longestSubstringWithoutDuplication(string str) {
  int pos = -1, len = -1, n = str.length(), counter = 0, l = 0, r = 0;
	unordered_map<char, int> mp;
	while(r < n) {
		if(++mp[str[r++]] == 2) counter++;
		while(counter) {
			if(--mp[str[l++]] == 1) counter--;
		}
		if(len < (r - l)) {
			len = r - l;
			pos = l;
		}
	}
  return str.substr(pos, len);
}