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Longest Substring Without Repeating Charactersmedium

Longest Substring Without Repeating Characters

medium Coding Interview Patterns 15–20 min

NumPy allowed · plain Python earns 10 bonus points

Interactive
Two Pointers & Sliding Window, Step by Step
Pattern
1
L
2
3
4
6
R
arr[L]=1 + arr[R]=6 = 7 vs target 6 -> too big, move R left
Step 1 / 3
Both modes run the exact algorithm described on the linked practice problem, one real step at a time -- not a pre-rendered animation. Edit the input and every step recomputes live.

Master the dynamic sliding window pattern: expand the right boundary and jump the left boundary using a character-to-last-seen-index hash map.

Related Skills

Task

Implement length_of_longest_substring(s): return the length of the longest substring of s that contains no duplicate characters.

Function Signature

length_of_longest_substring(s: str) -> int

Examples

Example 1: Repeating Pattern abc
Input: s = 'abcabcbb'
Output: 3
Example 2: All Characters Identical
Input: s = 'bbbbb'
Output: 1

Constraints

  • Libraries are allowed; a plain-Python solution earns 10 bonus points.
  • 0 <= len(s) <= 5 * 10^4.
  • s consists of English letters, digits, symbols, and spaces.
Python3Saved ✓
def length_of_longest_substring(s: str) -> int:
"""Return the length of the longest substring without repeating characters."""
# Your implementation here
pass

Case 1: Repeating Pattern abc
Input: s = 'abcabcbb'
Expected: 3
Case 2: All Characters Identical
Input: s = 'bbbbb'
Expected: 1