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2021/nim/day18.nim

@@ -0,0 +1,90 @@
+import ./common, std/[sequtils, algorithm, sugar, sets, strformat, strutils, tables, options]
+
+type
+  BinaryTreeNodePathSegment = enum left, right
+  BinaryTreeNodePath = seq[BinaryTreeNodePathSegment]
+  BinaryTreeNodeKind = enum
+    leaf
+    branch
+  BinaryTreeNode = ref BinaryTreeNodeObj
+  BinaryTreeNodeObj = object
+    case kind: BinaryTreeNodeKind
+    of leaf: value: uint64
+    of branch: left, right: BinaryTreeNode
+  BinaryTreeNodeParseResult = object
+    node: BinaryTreeNodeObj
+    parsed_length: uint64
+
+proc parseBinaryTree(s: string): (BinaryTreeNode, uint64) =
+  case s[0]:
+    of '0'..'9': result = (BinaryTreeNode(kind: leaf, value: uint8(s[0]) - uint8('0')), 1'u64)
+    of '[':
+      let (left, leftLen) = parseBinaryTree(s[1..^1])
+      let (right, righLen) = parseBinaryTree(s[2+leftLen..^1])
+      result = (BinaryTreeNode(kind: branch, left: left, right: right), 3'u64 + leftLen + righLen)
+    else:
+      echo "unexpected string"
+
+proc nodeAt(node: BinaryTreeNode, path: BinaryTreeNodePath): Option[BinaryTreeNode] =
+  var curNode = node
+  for p in path:
+    if curNode.kind == leaf: return none(BinaryTreeNode)
+    case p:
+      of left: curNode = node.left
+      of right: curNode = node.left
+  return some(curNode)
+
+proc crawlFor(node: BinaryTreeNode, predicate: (node: BinaryTreeNode, path: BinaryTreeNodePath) -> bool, path: BinaryTreeNodePath = @[]): Option[BinaryTreeNodePath] =
+  if node.predicate(path): return some(path)
+  elif node.kind == branch:
+    let lp = path & @[left]
+    let ln = node.left.crawlFor(predicate, lp)
+    if ln.isSome: return some(lp)
+    let rp = path & @[right]
+    let rn = node.right.crawlFor(predicate, rp)
+    if rn.isSome: return some(rp)
+  return none(BinaryTreeNodePath)
+
+when not defined(release):
+  let (bt, n) = parseBinaryTree("[[1,2],3]")
+  assert bt.right.value == 3'u64
+  assert bt.left.left.value == 1'u64
+  assert bt.left.right.value == 2'u64
+  assert n == 9
+
+proc valueLeftOf(node: var BinaryTreeNode, path: BinaryTreeNodePath): Option[BinaryTreeNodePath] =
+  # for every right in the given path ordered from deepest to shallowest
+  # go left at that point and find the right-most value if any
+  # if such a process fails to find anything, there's no possible value
+
+proc valueRightOf(node: var BinaryTreeNode, path: BinaryTreeNodePath): Option[BinaryTreeNodePath] =
+  # see valueLeftOf, but replace left<->right
+
+proc explodeAt(node: var BinaryTreeNode, path: BinaryTreeNodePath) =
+  # TODO: implement exploding
+
+proc splitAt(node: var BinaryTreeNode, path: BinaryTreeNodePath) =
+  # TODO: implement exploding
+
+proc p1(input: Lines): uint64 =
+  var (bt, _) = input[0].parseBinaryTree()
+  # TODO: iterate over the input, parsing into binary trees
+  # fold over the binary trees, creating a new btree with each child btree as children
+  # reduce that btree via explode/split rules
+  # calculate magnitude
+  let explodePath = bt.crawlFor((_, p) => p.len() > 4)
+  let splitPath = bt.crawlFor((n, _) => n.kind == leaf and n.value >= 10)
+
+const input = """
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]
+""".strip().split('\n').mapIt(it.strip)
+doDayX 18, (n: int) => n.loadInput, p1, p1, (input, 4140'u64, 0'u64)

2021/rust/day18.rs

@@ -50,8 +50,11 @@ fn maybe_explode<T: std::fmt::Debug>(tree: &mut BinaryTreeNode<T>) -> bool {
     }
 }
 
-fn parse_binary_tree(s: &str) -> Result<BinaryTreeNode<u64>, &'static str> {
-    let chars = s.chars().peekable();
+fn parse_binary_tree<'a, I>(str_iter: I) -> Result<BinaryTreeNode<u64>, &'static str> 
+where
+    I: Peekable<Item = &'a char>,
+{
+    let chars = str_iter.peekable();
     let ch = chars.peek();
     if let Some(c) = ch {
         match c {
@@ -72,7 +75,7 @@ fn parse_binary_tree(s: &str) -> Result<BinaryTreeNode<u64>, &'static str> {
 }
 
 fn main() {
-    let result = parse_binary_tree(&day_input(18));
+    let result = parse_binary_tree(day_input(18).chars());
     println!("Snailfish Homework: {:#?}", result);
 }