818. Race Car

中文文档

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.

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.

Solutions

Python3

Java

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