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# 1638. Count Substrings That Differ by One Character

<https://leetcode.com/problems/count-substrings-that-differ-by-one-character>

## Description

Given two strings `s` and `t`, find the number of ways you can choose a non-empty substring of `s` and replace a **single character** by a different character such that the resulting substring is a substring of `t`. In other words, find the number of substrings in `s` that differ from some substring in `t` by **exactly** one character.

For example, the underlined substrings in `"computer"` and `"computation"` only differ by the `'e'`/`'a'`, so this is a valid way.

Return *the number of substrings that satisfy the condition above.*

A **substring** is a contiguous sequence of characters within a string.

**Example 1:**

```
**Input:** s = "aba", t = "baba"
**Output:** 6
**Explanation:** The following are the pairs of substrings from s and t that differ by exactly 1 character:
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
The underlined portions are the substrings that are chosen from s and t.
```

​​**Example 2:**

```
**Input:** s = "ab", t = "bb"
**Output:** 3
**Explanation:** The following are the pairs of substrings from s and t that differ by 1 character:
("ab", "bb")
("ab", "bb")
("ab", "bb")
​​​​The underlined portions are the substrings that are chosen from s and t.
```

**Example 3:**

```
**Input:** s = "a", t = "a"
**Output:** 0
```

**Example 4:**

```
**Input:** s = "abe", t = "bbc"
**Output:** 10
```

**Constraints:**

* `1 <= s.length, t.length <= 100`
* `s` and `t` consist of lowercase English letters only.

## ac

```java
```