EasyNo. 1180LeetCode Premium
Count Substrings with Only One Distinct Letter — LeetCode 1180 Python Solution
- Pattern
- Math and Number Theory
- Topics
- Math, String
- Reading time
- 2 min
- Source
- leetcode.com
The problem
Given a string s, return the number of substrings that have only one distinct letter.
Example
- Input
- s = "aaaba"
- Output
- 8
- Explanation
- The substrings with one distinct letter are "aaa", "aa", "a", "b".
Python solution
class Solution:
def countLetters(self, s: str) -> int:
n = len(s)
i = ans = 0
while i < n:
j = i
while j < n and s[j] == s[i]:
j += 1
ans += (1 + j - i) * (j - i) // 2
i = j
return ansComplexity
- Time
- O(n)where n is the length of the string s
- Space · auxiliary
- O(1)
Pattern: Math and Number Theory
Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1180. Count Substrings with Only One Distinct Letter is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.
The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.
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Frequently asked questions
- How hard is LeetCode 1180. Count Substrings with Only One Distinct Letter?
LeetCode 1180. Count Substrings with Only One Distinct Letter is rated Easy on LeetCode.
- What is the time complexity of LeetCode 1180. Count Substrings with Only One Distinct Letter?
The Python solution on this page runs in O(n), where n is the length of the string s.
- What is the space complexity of LeetCode 1180. Count Substrings with Only One Distinct Letter?
The Python solution on this page uses O(1) auxiliary space.
- What topics does LeetCode 1180. Count Substrings with Only One Distinct Letter cover?
LeetCode 1180. Count Substrings with Only One Distinct Letter is tagged Math and String on LeetCode.
- Is LeetCode 1180. Count Substrings with Only One Distinct Letter a premium problem?
Yes. LeetCode 1180. Count Substrings with Only One Distinct Letter is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.