Race Car

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.

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