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# 0097. Interleaving String

<https://leetcode.com/problems/interleaving-string>

## Description

Given strings `s1`, `s2`, and `s3`, find whether `s3` is formed by an **interleaving** of `s1` and `s2`.

An **interleaving** of two strings `s` and `t` is a configuration where they are divided into **non-empty** substrings such that:

* `s = s1 + s2 + ... + sn`
* `t = t1 + t2 + ... + tm`
* `|n - m| <= 1`
* The **interleaving** is `s1 + t1 + s2 + t2 + s3 + t3 + ...` or `t1 + s1 + t2 + s2 + t3 + s3 + ...`

**Note:** `a + b` is the concatenation of strings `a` and `b`.

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/09/02/interleave.jpg)

```
**Input:** s1 = "aabcc", s2 = "dbbca", s3 = "aadbbcbcac"
**Output:** true
```

**Example 2:**

```
**Input:** s1 = "aabcc", s2 = "dbbca", s3 = "aadbbbaccc"
**Output:** false
```

**Example 3:**

```
**Input:** s1 = "", s2 = "", s3 = ""
**Output:** true
```

**Constraints:**

* `0 <= s1.length, s2.length <= 100`
* `0 <= s3.length <= 200`
* `s1`, `s2`, and `s3` consist of lowercase English letters.

**Follow up:** Could you solve it using only `O(s2.length)` additional memory space?

## ac

```java
```