day15

2 files changed, 101 insertions, 0 deletions

diff --git a/day15/example.txt b/day15/example.txt
new file mode 100644
index 0000000..4f58f74
--- /dev/null
+++ b/day15/example.txt
@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7
diff --git a/day15/solution.zig b/day15/solution.zig
new file mode 100644
index 0000000..eb6dcbe
--- /dev/null
+++ b/day15/solution.zig
@@ -0,0 +1,100 @@
+const std = @import("std");
+const print = std.debug.print;
+const assert = std.debug.assert;
+const ArrayList = std.ArrayList;
+const HashMap = std.HashMap;
+const mem = std.mem;
+
+const fin = mem.trim(u8, @embedFile("./input.txt"), &std.ascii.whitespace);
+var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+const allocator = gpa.allocator();
+
+fn hash(s: []const u8) u64 {
+    var h: u64 = 0;
+    for (s) |c| {
+        h += c;
+        h *= 17;
+        h %= 256;
+    }
+
+    return @bitCast(h);
+}
+
+fn part1(strings: []const []const u8) void {
+    var ans: u64 = 0;
+
+    for (strings) |s| {
+        ans += hash(s);
+    }
+
+    print("{d}\n", .{ans});
+}
+
+const Pair = struct {
+    label: []const u8,
+    value: u64,
+};
+
+fn part2(strings: []const []const u8) !void {
+    var map: [256]ArrayList(Pair) = undefined;
+
+    for (&map) |*e| {
+        e.* = ArrayList(Pair).init(allocator);
+    }
+
+    for (strings) |s| {
+        const action = s[mem.indexOfAny(u8, s, "-=").?];
+        var toks = mem.tokenizeAny(u8, s, "-=");
+        const label = toks.next().?;
+        const value = toks.next();
+
+        if (action == '=') {
+            const v = try std.fmt.parseInt(u64, value.?, 10);
+            const m = &map[hash(label)];
+            for (m.items) |*i| {
+                if (mem.eql(u8, i.label, label)) {
+                    i.value = v;
+                    break;
+                }
+            } else {
+                try map[hash(label)].append(Pair{
+                    .value = v,
+                    .label = label,
+                });
+            }
+        } else {
+            var m = &map[hash(label)];
+            for (m.items, 0..) |e, i| {
+                if (mem.eql(u8, e.label, label)) {
+                    _ = m.orderedRemove(i);
+                    break;
+                }
+            }
+        }
+    }
+
+    var ans: u64 = 0;
+    for (map, 1..) |m, i| {
+        for (m.items, 1..) |e, j| {
+            ans += i * j * e.value;
+        }
+    }
+
+    print("{d}\n", .{ans});
+}
+
+pub fn solve(strings: []const []const u8) !void {
+    part1(strings);
+    try part2(strings);
+}
+
+pub fn main() !void {
+    var splitComma = mem.splitScalar(u8, fin, ',');
+    var strings = ArrayList([]const u8).init(allocator);
+
+    while (splitComma.next()) |s| {
+        try strings.append(s);
+    }
+
+    try solve(strings.items);
+}