Sliding Window — Variable LeetCode 3

Longest Substring Without Repeating Characters / visualized

right always moves forward. left only moves when it has to — when the character entering the window is already inside it. A HashSet tracks exactly what's currently in the window, so checking "is this a duplicate?" is O(1).

String

Execution

idle

Press Run to begin.

0 / 0

Speed

Java · running line

in window duplicate / shrinking new max

O(n) time · O(min(n, charset)) space · each character enters and leaves the window at most once — that's what makes it O(n), not O(n²).