Day 9

Leaderboard position: 124 & 365

answers/09.txt

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+388131
+3239376988

data/09.txt

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+459 players; last marble is worth 72103 points

day09.nim

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+import lists, math, sequtils, strscans, strutils
+
+func insertAfter(node: DoublyLinkedNode[int], value: int) =
+    var newNode = newDoublyLinkedNode(value)
+    newNode.next = node.next
+    newNode.prev = node
+    newNode.next.prev = newNode
+    newNode.prev.next = newNode
+
+func remove(node: DoublyLinkedNode[int]) =
+    node.prev.next = node.next
+    node.next.prev = node.prev
+
+func newSingleNode(value: int): DoublyLinkedNode[int] =
+    result = newDoublyLinkedNode(value)
+    result.next = result
+    result.prev = result
+
+var
+    input = readFile("data/09.txt").strip
+    players: int
+    marbles: int
+
+if not input.scanf("$i players; last marble is worth $i points", players, marbles):
+    raise newException(Defect,  "Invalid input line: " & input)
+
+var
+    player = 0
+    scores = newSeq[int](players)
+    current = newSingleNode(0)
+
+for i in 1..marbles*100:
+    if i mod 23 == 0:
+        current = current.prev.prev.prev.prev.prev.prev.prev
+        scores[player] += i + current.value
+        current.remove
+        current = current.next
+    else:
+        current.next.insertAfter(i)
+        current = current.next.next
+
+    player = (player + 1) mod players
+
+    if i == marbles or i == marbles * 100:
+        echo scores.max