Given a string, find the length of the longest substring without repeating characters.Examples:
Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
Solve this with a sliding window. Keep record of the leftmost and iterate with a pointer serving as the rightmost. As long as we find a repeating character(hash), we move the leftmost one step right.