Idea

• Use sliding window
  • 2 pointers, right pointer to expand the window, left pointer to reduce the window
  • Shrink the window when there is repeated character until there isn't repeated characters

Space & time analysis

• Time O(n), each character will be processed once, and at most pop out once

• Space O(n), the given string may contain all unique characters

• 1st attempt (Go)

• 2nd attempt (Java) (28mins) ❤️

• 3rd attempt (java) (sliding window rusty)

• 4th attempt (java)❤️❤️