1 files changed, 77 insertions, 0 deletions
diff --git a/src/03/main.zig b/src/03/main.zig
new file mode 100644
index 0000000..2ec8f24
--- /dev/null
+++ b/src/03/main.zig
@@ -0,0 +1,77 @@
+const std = @import("std");
+const aoc = @import("aoc");
+
+const Entry = []u1;
+const Vector = struct { x: u16, y: u16 };
+
+fn freeEntries(allocator: std.mem.Allocator, entries: *const std.ArrayList(Entry)) void {
+    for (entries.items) |entry| {
+        allocator.free(entry);
+    }
+    entries.deinit();
+}
+
+fn parse(allocator: std.mem.Allocator, input: []u8) !std.ArrayList(Entry) {
+    var entries = std.ArrayList(Entry).init(allocator);
+    errdefer freeEntries(allocator, &entries);
+
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    while (lineit.next()) |line| {
+        var linemap: []u1 = try allocator.alloc(u1, line.len);
+        errdefer allocator.free(linemap);
+
+        for (line) |c, i| {
+            linemap[i] = @boolToInt(c == '#');
+        }
+        try entries.append(linemap);
+    }
+
+    return entries;
+}
+
+fn treesHit(map: std.ArrayList(Entry), slope: Vector) u16 {
+    var count: u16 = 0;
+    var pos = Vector{ .x = 0, .y = 0 };
+    while (pos.y < map.items.len - 1) {
+        pos.x += slope.x;
+        pos.y += slope.y;
+
+        count += map.items[pos.y][pos.x % map.items[0].len];
+    }
+    return count;
+}
+
+fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    const map = try parse(allocator, input);
+    defer freeEntries(allocator, &map);
+
+    const answer = treesHit(map, Vector{ .x = 3, .y = 1 });
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
+}
+
+fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    const map = try parse(allocator, input);
+    defer freeEntries(allocator, &map);
+
+    const slopes = [_]Vector{
+        Vector{ .x = 1, .y = 1 },
+        Vector{ .x = 3, .y = 1 },
+        Vector{ .x = 5, .y = 1 },
+        Vector{ .x = 7, .y = 1 },
+        Vector{ .x = 1, .y = 2 },
+    };
+
+    var answer: u32 = 1;
+    for (slopes) |slope| {
+        answer *= treesHit(map, slope);
+    }
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
+}
+
+pub const main = aoc.main(part1, part2, .{ "282", "958815792" });