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Back to Problems

1180. Count Substrings with Only One Distinct Letter

Easy80.2% AcceptancePremium
MathString
Asked by:Virtu Financial
ProblemHints (3)SolutionsVideosCompanies (1)Notes

Problem Statement

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V

This is a premium problem. We're working on making it available for free soon.

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Problem Hints

Use these hints if you're stuck. Try solving on your own first.

1
Hint 1

What if we divide the string into substrings containing only one distinct character with maximal lengths?

2
Hint 2

Now that you have sub-strings with only one distinct character, Try to come up with a formula that counts the number of its sub-strings.

3
Hint 3

Alternatively, Observe that the constraints are small so you can use brute force.

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Longest Substring Without Repeating Characters - Leetcode 3 - Python

NeetCode
6:46657,697 views

Asked By Companies

1 companies
V
Virtu Financial

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0 characters

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Related Topics

MathString

Problem Stats

Acceptance Rate80.2%
DifficultyEasy
Companies1

Practice on LeetCode

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Frequently Asked Questions

Why does the formula k*(k+1)/2 work in this problem?

A sequence of k identical characters can form substrings of length 1 through k. The number of such substrings follows the arithmetic series 1 + 2 + ... + k, which simplifies to k*(k+1)/2.

Is Count Substrings with Only One Distinct Letter asked in coding interviews?

Yes, similar substring counting problems appear in coding interviews at companies like Amazon and Google. They test your understanding of string traversal, pattern observation, and converting brute-force ideas into linear-time solutions.

What data structure is best for Count Substrings with Only One Distinct Letter?

No special data structure is required. A simple variable to track the current run length of identical characters is enough, making the solution space-efficient.

What is the optimal approach for Count Substrings with Only One Distinct Letter?

The optimal approach scans the string and counts lengths of consecutive identical characters. For each block of length k, the number of valid substrings is k*(k+1)/2. Summing this for all blocks gives the total in O(n) time.