LeetCode/problems/minimum-number-of-refueling-stops.kt

import java.util.PriorityQueue

class Solution {
    fun minRefuelStops(target: Int, startFuel: Int, stations: Array<IntArray>): Int {
        var maxReach = startFuel
        val availableRefuelling = PriorityQueue<Int>(reverseOrder())

        var refuelled = 0
        var i = 0

        while (maxReach < target) {
            while (i < stations.size && stations[i][0] <= maxReach) {
                // keep track of possible refuels
                availableRefuelling.add(stations[i][1])
                i++
            }

            if (availableRefuelling.isEmpty()) {
                // no refuels are available and target has not been reached
                return -1
            }


            // refuel at least once in order to progress
            maxReach += availableRefuelling.poll()!!
            refuelled++
        }
        return refuelled
    }
}

fun main() {
    val s = Solution()

    check(s.minRefuelStops(1, 1, arrayOf()) == 0)
    check(s.minRefuelStops(100, 1, arrayOf(intArrayOf(10, 100))) == -1)
    check(
        s.minRefuelStops(
            100, 10, arrayOf(intArrayOf(10, 60), intArrayOf(20, 30), intArrayOf(30, 30), intArrayOf(60, 40))
        ) == 2
    )
    check(
        s.minRefuelStops(
            1000, 299,
            arrayOf(
                intArrayOf(13, 21),
                intArrayOf(26, 115),
                intArrayOf(100, 47),
                intArrayOf(225, 99),
                intArrayOf(299, 141),
                intArrayOf(444, 198),
                intArrayOf(608, 190),
                intArrayOf(636, 157),
                intArrayOf(647, 255),
                intArrayOf(841, 123)
            )
        ) == 4
    )
}