# 0686. Repeated String Match

<https://leetcode.com/problems/repeated-string-match>

## Description

Given two strings `a` and `b`, return the minimum number of times you should repeat string `a` so that string `b` is a substring of it. If it is impossible for `b`​​​​​​ to be a substring of `a` after repeating it, return `-1`.

**Notice:** string `"abc"` repeated 0 times is `""`,  repeated 1 time is `"abc"` and repeated 2 times is `"abcabc"`.

**Example 1:**

```
**Input:** a = "abcd", b = "cdabcdab"
**Output:** 3
**Explanation:** We return 3 because by repeating a three times "ab**cdabcdab**cd", b is a substring of it.
```

**Example 2:**

```
**Input:** a = "a", b = "aa"
**Output:** 2
```

**Example 3:**

```
**Input:** a = "a", b = "a"
**Output:** 1
```

**Example 4:**

```
**Input:** a = "abc", b = "wxyz"
**Output:** -1
```

**Constraints:**

* `1 <= a.length <= 104`
* `1 <= b.length <= 104`
* `a` and `b` consist of lower-case English letters.

## ac

```java
```