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. Now for some target position, say 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. Note: 1 <= target <= 10000.