What is the time complexity of LeetCode 2743. Count Substrings Without Repeating Character?

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

What is the space complexity of LeetCode 2743. Count Substrings Without Repeating Character?

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

Count Substrings Without Repeating Character — LeetCode 2743 Python Solution

MediumLeetCode PremiumHash TableStringSliding Window

Problem: #2743
Pattern: Sliding Window
Reading time: 2 min
Source: leetcode.com

The problem

You are given a string s consisting only of lowercase English letters. We call a substring special if it contains no character which has occurred at least twice (in other words, it does not contain a repeating character).

Example

Input: s = "abcd"
Output: 10
Explanation: Since each character occurs once, every substring is a special substring. We have 4 substrings of length one, 3 of length two, 2 of length three, and 1 substring of length four. So overall there are 4 + 3 + 2 + 1 = 10 special substrings.

Python solution

Python

class Solution:
    def numberOfSpecialSubstrings(self, s: str) -> int:
        cnt = Counter()
        ans = j = 0
        for i, c in enumerate(s):
            cnt[c] += 1
            while cnt[c] > 1:
                cnt[s[j]] -= 1
                j += 1
            ans += i - j + 1
        return ans

Complexity

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

Pattern: Sliding Window

Collapse a nested loop over every subarray into a single pass with two indices. LeetCode 2743. Count Substrings Without Repeating Character 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 2743. Count Substrings Without Repeating Character?: LeetCode 2743. Count Substrings Without Repeating Character is rated Medium on LeetCode.
What is the time complexity of LeetCode 2743. Count Substrings Without Repeating Character?: The Python solution on this page runs in O(n).
What is the space complexity of LeetCode 2743. Count Substrings Without Repeating Character?: The Python solution on this page uses O(C) auxiliary space.
What topics does LeetCode 2743. Count Substrings Without Repeating Character cover?: LeetCode 2743. Count Substrings Without Repeating Character is tagged Hash Table, String and Sliding Window on LeetCode.
Is LeetCode 2743. Count Substrings Without Repeating Character a premium problem?: Yes. LeetCode 2743. Count Substrings Without Repeating Character is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.