Longest Substring Without Repeating Characters

LeetCode 3 • Medium • Sliding Window

Find the length of the longest substring without repeating characters.
Input: s = "abcabcbb" → Output: 3 (substring "abc")

TimeO(n)each char at most 2x

SpaceO(min(n,128))char set

Window

Right (expand)

Shrink

Result

Window

—

Set

—

MaxLen

—

Speed:

Ready

Press Play. Expand right, add char to set. If duplicate, shrink from left until unique. Track max length.

⌨ Type It

Practice until you don't need to look. The green highlights are the nuances to burn into memory.

═══ LONGEST SUBSTRING WITHOUT REPEATING — SLIDING WINDOW ═══

PATTERN ▸ Sliding window + set (shrink when duplicate) O(n) · O(min(n,128))

① INIT

left=0, char_set=set(), result=0

② EXPAND RIGHT

for right in range(len(s)):

③ SHRINK WHILE DUPLICATE

while s[right] in char_set:

char_set.remove(s[left]); left += 1

④ ADD & UPDATE

char_set.add(s[right])

result = max(result, right - left + 1)

⑤ RETURN

return result

▼ your implementation ▼