problems: add „871. Minimum Number of Refueling Stops“

Signed-off-by: Matej Focko <mfocko@redhat.com>

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

@@ -0,0 +1,59 @@
+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
+    )
+}