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g0801_0900.s0818_race_car.readme.md Maven / Gradle / Ivy

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:
    *   `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