How hard is LeetCode 2953. Count Complete Substrings?

LeetCode 2953. Count Complete Substrings is rated Hard on LeetCode.

What is the time complexity of LeetCode 2953. Count Complete Substrings?

The Python solution on this page runs in O(n \times |\Sigma|).

What is the space complexity of LeetCode 2953. Count Complete Substrings?

The Python solution on this page uses O(|\Sigma|), where n is the length of the string word; and \Sigma is the size of the character set auxiliary space.

What topics does LeetCode 2953. Count Complete Substrings cover?

LeetCode 2953. Count Complete Substrings is tagged Hash Table, String and Sliding Window on LeetCode.

Count Complete Substrings — LeetCode 2953 Python Solution

HardHash TableStringSliding Window

Problem: #2953
Pattern: Sliding Window
Reading time: 6 min
Source: leetcode.com

The problem

You are given a string word and an integer k. A substring s of word is complete if: Each character in s occurs exactly k times.

Example

Input: word = "igigee", k = 2
Output: 3
Explanation: The complete substrings where each character appears exactly twice and the difference between adjacent characters is at most 2 are: igigee, igigee, igigee.

Python solution

Python

class Solution:
    def countCompleteSubstrings(self, word: str, k: int) -> int:
        def f(s: str) -> int:
            m = len(s)
            ans = 0
            for i in range(1, 27):
                l = i * k
                if l > m:
                    break
                cnt = Counter(s[:l])
                freq = Counter(cnt.values())
                ans += freq[k] == i
                for j in range(l, m):
                    freq[cnt[s[j]]] -= 1
                    cnt[s[j]] += 1
                    freq[cnt[s[j]]] += 1

                    freq[cnt[s[j - l]]] -= 1
                    cnt[s[j - l]] -= 1
                    freq[cnt[s[j - l]]] += 1

                    ans += freq[k] == i
            return ans

        n = len(word)
        ans = i = 0
        while i < n:
            j = i + 1
            while j < n and abs(ord(word[j]) - ord(word[j - 1])) <= 2:
                j += 1
            ans += f(word[i:j])
            i = j
        return ans

Complexity

Measure	Complexity
Time	O(n \times \|\Sigma\|)
Space	O(\|\Sigma\|), where n is the length of the string word; and \Sigma is the size of the character set auxiliary

Pattern: Sliding Window

Collapse a nested loop over every subarray into a single pass with two indices. LeetCode 2953. Count Complete Substrings 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 2953. Count Complete Substrings?: LeetCode 2953. Count Complete Substrings is rated Hard on LeetCode.
What is the time complexity of LeetCode 2953. Count Complete Substrings?: The Python solution on this page runs in O(n \times |\Sigma|).
What is the space complexity of LeetCode 2953. Count Complete Substrings?: The Python solution on this page uses O(|\Sigma|), where n is the length of the string word; and \Sigma is the size of the character set auxiliary space.
What topics does LeetCode 2953. Count Complete Substrings cover?: LeetCode 2953. Count Complete Substrings is tagged Hash Table, String and Sliding Window on LeetCode.