What is the time complexity of LeetCode 340. Longest Substring with At Most K Distinct Characters?

The Python solution on this page runs in O(n).

What is the space complexity of LeetCode 340. Longest Substring with At Most K Distinct Characters?

The Python solution on this page uses O(k) auxiliary space.

Longest Substring with At Most K Distinct Characters — LeetCode 340 Python Solution

MediumLeetCode PremiumHash TableStringSliding Window

Problem: #340
Pattern: Sliding Window
Reading time: 2 min
Source: leetcode.com

The problem

Given a string s and an integer k, return the length of the longest substring of s that contains at most k distinct characters.

Example

Input: s = "eceba", k = 2
Output: 3
Explanation: The substring is "ece" with length 3.

Python solution

Python

class Solution:
    def lengthOfLongestSubstringKDistinct(self, s: str, k: int) -> int:
        l = 0
        cnt = Counter()
        for c in s:
            cnt[c] += 1
            if len(cnt) > k:
                cnt[s[l]] -= 1
                if cnt[s[l]] == 0:
                    del cnt[s[l]]
                l += 1
        return len(s) - l

Complexity

Measure	Complexity
Time	O(n)
Space	O(k) auxiliary

Pattern: Sliding Window

Collapse a nested loop over every subarray into a single pass with two indices. LeetCode 340. Longest Substring with At Most K Distinct Characters is filed here because LeetCode tags it Sliding Window, which is the vocabulary this hub collects.

The sliding window guide has the Python template for the pattern and the 116 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 340. Longest Substring with At Most K Distinct Characters?: LeetCode 340. Longest Substring with At Most K Distinct Characters is rated Medium on LeetCode.
What is the time complexity of LeetCode 340. Longest Substring with At Most K Distinct Characters?: The Python solution on this page runs in O(n).
What is the space complexity of LeetCode 340. Longest Substring with At Most K Distinct Characters?: The Python solution on this page uses O(k) auxiliary space.
What topics does LeetCode 340. Longest Substring with At Most K Distinct Characters cover?: LeetCode 340. Longest Substring with At Most K Distinct Characters is tagged Hash Table, String and Sliding Window on LeetCode.
Is LeetCode 340. Longest Substring with At Most K Distinct Characters a premium problem?: Yes. LeetCode 340. Longest Substring with At Most K Distinct Characters is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.