LeetCode in Kotlin

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 = 1Your 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

Solution

import java.util.LinkedList
import java.util.Queue

class Solution {
    fun racecar(target: Int): Int {
        val queue: Queue<IntArray> = LinkedList()
        queue.add(intArrayOf(0, 1, 0))
        while (queue.isNotEmpty()) {
            val arr = queue.poll()
            if (arr[0] == target) {
                return arr[2]
            }
            queue.add(intArrayOf(arr[0] + arr[1], 2 * arr[1], 1 + arr[2]))
            if (arr[0] + arr[1] > target && arr[1] > 0) {
                queue.add(intArrayOf(arr[0], -1, 1 + arr[2]))
            }
            if (arr[0] + arr[1] < target && arr[1] < 0) {
                queue.add(intArrayOf(arr[0], 1, 1 + arr[2]))
            }
        }
        return -1
    }
}

This site is open source. Improve this page.