818 - Race Car.

Hard

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:

• When you get an instruction 'R', your car does the following:

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:

• <code>1 <= target <= 10⁴</code>