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13. Longest Substring Without Repeating Characters

mediumAsked at Squarespace

Find the length of the longest substring of distinct characters; Squarespace uses it to test the sliding-window pattern.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given a string s, return the length of the longest substring that contains no repeating characters. Substrings must be contiguous.

Constraints

  • 0 <= s.length <= 5 * 10^4
  • s consists of English letters, digits, symbols and spaces

Examples

Example 1

Input
s="abcabcbb"
Output
3

Example 2

Input
s="bbbbb"
Output
1

Approaches

1. All substrings check

Enumerate every substring and verify uniqueness with a set.

Time
O(n^3)
Space
O(n)
let best=0;
for(let i=0;i<n;i++) for(let j=i;j<n;j++){
  const set=new Set(s.slice(i,j+1));
  if(set.size===j-i+1) best=Math.max(best,j-i+1);
}
return best;

Tradeoff:

2. Sliding window with last-seen map

Move a right pointer forward while jumping the left pointer past any prior occurrence. Linear time, alphabet-sized space.

Time
O(n)
Space
O(k)
function lengthOfLongestSubstring(s) {
  const last = new Map();
  let l = 0, best = 0;
  for (let r = 0; r < s.length; r++) {
    if (last.has(s[r]) && last.get(s[r]) >= l) l = last.get(s[r]) + 1;
    last.set(s[r], r);
    best = Math.max(best, r - l + 1);
  }
  return best;
}

Tradeoff:

Squarespace-specific tips

Squarespace likes when you connect this sliding window to their rate-limited publish API that windows requests per site over a moving interval.

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Output

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