Day 6.2

06/src/main.zig

@@ -12,6 +12,7 @@ const Node = struct {
 };
 
 const Links = std.ArrayList(Link);
+const NodeList = std.ArrayList(*Node);
 const Nodes = std.StringHashMap(*Node);
 
 fn parse(alloc: *std.mem.Allocator, stream: *std.fs.File.InStream.Stream) !Links {
@@ -21,7 +22,6 @@ fn parse(alloc: *std.mem.Allocator, stream: *std.fs.File.InStream.Stream) !Links
 
     while (try stream.readUntilDelimiterOrEof(&buf, '\n')) |line| {
         std.debug.assert(line.len == 7 and line[3] == ')');
-        std.debug.warn("{}\n", line);
 
         var out: Link = Link{};
         std.mem.copy(u8, &out.a, line[0..3]);
@@ -48,6 +48,22 @@ fn getOrCreateNode(alloc: *std.mem.Allocator, nodes: var, name: [3]u8) !*Node {
     }
 }
 
+fn getParents(alloc: *std.mem.Allocator, node: *Node) !NodeList {
+    var out = NodeList.init(alloc);
+    var n: *Node = node;
+    while (n.parent) |p| {
+        try out.append(p);
+        n = p;
+    }
+
+    return out;
+}
+
+// Assumes n1 is a parent of n2
+fn distance(n1: *Node, n2: *Node) u32 {
+    return n2.depth - n1.depth - 1;
+}
+
 pub fn main() anyerror!void {
     var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
     defer arena.deinit();
@@ -58,8 +74,6 @@ pub fn main() anyerror!void {
 
     var links = try parse(alloc, stream);
 
-    std.debug.warn("Part 1: {} links\n", links.len);
-
     // name -> node
     var nodes = Nodes.init(alloc);
 
@@ -76,8 +90,6 @@ pub fn main() anyerror!void {
         var a = try getOrCreateNode(alloc, &nodes, link.a);
         var b = try getOrCreateNode(alloc, &nodes, link.b);
 
-        std.debug.warn("\t{} ) {}\n", a.name, b.name);
-
         std.debug.assert(b.parent == null);
         b.parent = a;
     }
@@ -99,4 +111,28 @@ pub fn main() anyerror!void {
     }
 
     std.debug.warn("Part 1: {}\n", count);
+
+    // We need to find the node that both you and santa have in common
+
+    var you = (nodes.get("YOU") orelse unreachable).value;
+    var san = (nodes.get("SAN") orelse unreachable).value;
+
+    var yP = try getParents(alloc, you);
+    var sP = try getParents(alloc, san);
+
+    var inCommon = NodeList.init(alloc);
+
+    for (yP.toSlice()) |p1| {
+        for (sP.toSlice()) |p2| {
+            if (p1 == p2) try inCommon.append(p1);
+        }
+    }
+
+    std.debug.warn("Part 2: you have {} parents, santa has {}, {} in common\n", yP.count(), sP.count(), inCommon.count());
+
+    for (inCommon.toSlice()) |p| {
+        const d1 = distance(p, you);
+        const d2 = distance(p, san);
+        std.debug.warn("\t{} - ({}) {} ({}) - {}: {}\n", you.name, d1, p.name, d2, san.name, d1 + d2);
+    }
 }