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