1 files changed, 136 insertions, 0 deletions
diff --git a/src/day04.zig b/src/day04.zig
new file mode 100644
index 0000000..ba6aaf8
--- /dev/null
+++ b/src/day04.zig
@@ -0,0 +1,136 @@
+const std = @import("std");
+const mecha = @import("mecha");
+const print = std.debug.print;
+
+pub fn solve(part: []u8, buffer: []u8, allocator: std.mem.Allocator) !void {
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(buffer, allocator);
+    } else {
+        try part2(buffer, allocator);
+    }
+}
+
+fn amount(line: []const u8, allocator: std.mem.Allocator) usize {
+    const match = mecha.oneOf(.{ mecha.string("XMAS"), mecha.string("SAMX") });
+
+    var rest = line;
+    var output: usize = 0;
+    while (rest.len > 0) {
+        _ = match.parse(allocator, rest) catch {
+            rest = rest[1..];
+            continue;
+        };
+        rest = rest[3..];
+        output += 1;
+    }
+    return output;
+}
+
+fn diagonal(list: []const []const u8, startr: usize, startc: usize, dirr: i32, dirc: i32, allocator: std.mem.Allocator) !usize {
+    var line = std.ArrayList(u8).init(allocator);
+    defer line.deinit();
+
+    const rows: i32 = @intCast(list.len);
+    const width: i32 = @intCast(list[0].len);
+
+    var r: i32 = @intCast(startr);
+    var c: i32 = @intCast(startc);
+    while (r >= 0 and c >= 0 and r < rows and c < width) {
+        try line.append(list[@intCast(r)][@intCast(c)]);
+
+        r += dirr;
+        c += dirc;
+    }
+    return amount(line.items, allocator);
+}
+
+fn part1(buffer: []const u8, allocator: std.mem.Allocator) !void {
+    var lines = std.mem.splitScalar(u8, buffer, '\n');
+
+    var list = std.ArrayList([]const u8).init(allocator);
+    defer list.deinit();
+
+    var sum: usize = 0;
+
+    while (lines.next()) |line| {
+        if (line.len > 0) {
+            try list.append(line);
+            sum += amount(line, allocator); // HORIZONTAL
+        }
+    }
+
+    for (0..list.items.len) |r| {
+        sum += try diagonal(list.items, r, 0, -1, 1, allocator); // UP-RIGHT
+        sum += try diagonal(list.items, r, 0, 1, 1, allocator); // DOWN-RIGHT
+    }
+
+    for (1..list.items[0].len) |c| {
+        sum += try diagonal(list.items, 0, c, 1, 1, allocator); // DOWN-RIGHT
+        sum += try diagonal(list.items, list.items.len - 1, c, -1, 1, allocator); // UP-RIGHT
+    }
+
+    for (0..list.items[0].len) |c| { // VERTICAL
+        sum += try diagonal(list.items, 0, c, 1, 0, allocator);
+    }
+
+    print("{d}\n", .{sum});
+}
+
+//------------------------------PART 2---------------------------------------
+
+fn diagonal2(list: []const []const u8, startr: usize, startc: usize, dirr: i32, dirc: i32, allocator: std.mem.Allocator, hashmap: anytype) !usize {
+    var line = std.ArrayList(u8).init(allocator);
+    defer line.deinit();
+
+    const rows: i32 = @intCast(list.len);
+    const width: i32 = @intCast(list[0].len);
+    var output: usize = 0;
+
+    var r: i32 = @intCast(startr);
+    var c: i32 = @intCast(startc);
+    while (r >= 0 and c >= 0 and r < rows and c < width) {
+        try line.append(list[@intCast(r)][@intCast(c)]);
+
+        if (line.items.len >= 3 and (std.mem.eql(u8, line.items[line.items.len - 3 ..], "MAS") or std.mem.eql(u8, line.items[line.items.len - 3 ..], "SAM"))) {
+            if (hashmap.contains((r - dirr) * rows + (c - dirc))) {
+                output += 1;
+            } else {
+                try hashmap.put((r - dirr) * rows + (c - dirc), 1);
+            }
+        }
+
+        r += dirr;
+        c += dirc;
+    }
+    return output;
+}
+
+fn part2(buffer: []const u8, allocator: std.mem.Allocator) !void {
+    var map = std.AutoHashMap(i32, usize).init(allocator);
+    defer map.deinit();
+
+    var lines = std.mem.splitScalar(u8, buffer, '\n');
+
+    var list = std.ArrayList([]const u8).init(allocator);
+    defer list.deinit();
+
+    var sum: usize = 0;
+
+    while (lines.next()) |line| {
+        if (line.len > 0) {
+            try list.append(line);
+        }
+    }
+
+    for (0..list.items.len) |r| {
+        sum += try diagonal2(list.items, r, 0, -1, 1, allocator, &map); // UP-RIGHT
+        sum += try diagonal2(list.items, r, 0, 1, 1, allocator, &map); // DOWN-RIGHT
+    }
+
+    for (1..list.items[0].len) |c| {
+        sum += try diagonal2(list.items, 0, c, 1, 1, allocator, &map); // DOWN-RIGHT
+        sum += try diagonal2(list.items, list.items.len - 1, c, -1, 1, allocator, &map); // UP-RIGHT
+    }
+
+    print("{d}\n", .{sum});
+}