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# 1071. Greatest Common Divisor of Strings

<https://leetcode.com/problems/greatest-common-divisor-of-strings>

## Description

For two strings `s` and `t`, we say "`t` divides `s`" if and only if `s = t + ... + t`  (`t` concatenated with itself 1 or more times)

Given two strings str1 and str2, return the largest string `x` such that `x` divides both `str1` and `str2`.

**Example 1:**

```
**Input:** str1 = "ABCABC", str2 = "ABC"
**Output:** "ABC"
```

**Example 2:**

```
**Input:** str1 = "ABABAB", str2 = "ABAB"
**Output:** "AB"
```

**Example 3:**

```
**Input:** str1 = "LEET", str2 = "CODE"
**Output:** ""
```

**Example 4:**

```
**Input:** str1 = "ABCDEF", str2 = "ABC"
**Output:** ""
```

**Constraints:**

* `1 <= str1.length <= 1000`
* `1 <= str2.length <= 1000`
* `str1` and `str2` consist of English uppercase letters.

## ac

```java
```