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# 0818. Race Car

<https://leetcode.com/problems/race-car>

## Description

Your car starts at position `0` and speed `+1` on an infinite number line. Your car can go into negative positions. Your car drives automatically according to a sequence of instructions `'A'` (accelerate) and `'R'` (reverse):

* When you get an instruction `'A'`, your car does the following:
  * `position += speed`
  * `speed *= 2`
* When you get an instruction `'R'`, your car does the following:
  * If your speed is positive then `speed = -1`
  * otherwise `speed = 1` Your position stays the same.

For example, after commands `"AAR"`, your car goes to positions `0 --> 1 --> 3 --> 3`, and your speed goes to `1 --> 2 --> 4 --> -1`.

Given a target position `target`, return *the length of the shortest sequence of instructions to get there*.

**Example 1:**

```
**Input:** target = 3
**Output:** 2
**Explanation:** 
The shortest instruction sequence is "AA".
Your position goes from 0 --> 1 --> 3.
```

**Example 2:**

```
**Input:** target = 6
**Output:** 5
**Explanation:** 
The shortest instruction sequence is "AAARA".
Your position goes from 0 --> 1 --> 3 --> 7 --> 7 --> 6.
```

**Constraints:**

* `1 <= target <= 104`

## ac

```java
```