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# 1180. Count Substrings with Only One Distinct Letter

<https://leetcode.com/problems/count-substrings-with-only-one-distinct-letter>

## Description

Given a string `s`, return *the number of substrings that have only **one distinct** letter*.

**Example 1:**

```
**Input:** s = "aaaba"
**Output:** 8
**Explanation:** The substrings with one distinct letter are "aaa", "aa", "a", "b".
"aaa" occurs 1 time.
"aa" occurs 2 times.
"a" occurs 4 times.
"b" occurs 1 time.
So the answer is 1 + 2 + 4 + 1 = 8.
```

**Example 2:**

```
**Input:** s = "aaaaaaaaaa"
**Output:** 55
```

**Constraints:**

* `1 <= s.length <= 1000`
* `s[i]` consists of only lowercase English letters.

## ac

```java
```