visualization

Sliding Window

Grow greedily, shrink only when the window breaks.

s = "forgecode" · longest substring without repeating charactersstep 1/21

chars in window

empty

Empty window over "forgecode". L and R both start at index 0; the set of window chars is empty.

pseudocode

seen = set(); L = 0; best = 0
for R in range(len(s)):
    while s[R] in seen:
        seen.remove(s[L]); L += 1
    seen.add(s[R])
    best = max(best, R - L + 1)
return best