1 files changed, 123 insertions, 0 deletions
diff --git a/src/day08.zig b/src/day08.zig
new file mode 100644
index 0000000..2e356d9
--- /dev/null
+++ b/src/day08.zig
@@ -0,0 +1,123 @@
+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 {
+    var lookup: [256]std.ArrayList(std.meta.Tuple(&.{ i32, i32 })) = undefined;
+    for (&lookup) |*element| {
+        element.* = std.ArrayList(std.meta.Tuple(&.{ i32, i32 })).init(allocator);
+        errdefer element.*.deinit();
+    }
+
+    var lines = std.mem.splitScalar(u8, buffer, '\n');
+    const width: usize = lines.next().?.len;
+    lines.reset();
+    const distinct: [][]bool = try allocator.alloc([]bool, width * width);
+    defer allocator.free(distinct);
+    for (distinct) |*r| {
+        r.* = try allocator.alloc(bool, width);
+        @memset(r.*, false);
+    }
+
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(&lookup, distinct, &lines, width);
+    } else {
+        try part2(&lookup, distinct, &lines, width);
+    }
+
+    for (&lookup) |*element| {
+        element.*.deinit();
+    }
+
+    for (distinct) |r| {
+        allocator.free(r);
+    }
+}
+
+fn part1(lookup: *[256]std.ArrayList(std.meta.Tuple(&.{ i32, i32 })), distinct: [][]bool, lines: *std.mem.SplitIterator(u8, .scalar), width: usize) !void {
+    var row: i32 = 0;
+    var total_distinct: usize = 0;
+    while (lines.next()) |line| : (row += 1) {
+        if (line.len == 0) break;
+
+        var col: i32 = 0;
+        for (line) |item| {
+            if (item == '.' or item == '#') {
+                col += 1;
+                continue;
+            }
+
+            for (lookup[item].items) |antenna| {
+                const diffr = row - antenna[0];
+                const diffc = col - antenna[1];
+
+                const newr1 = antenna[0] - diffr;
+                const newc1 = antenna[1] - diffc;
+                if (newr1 >= 0 and newc1 >= 0 and newc1 < width and !distinct[@intCast(newr1)][@intCast(newc1)]) {
+                    distinct[@intCast(newr1)][@intCast(newc1)] = true;
+                    total_distinct += 1;
+                }
+
+                const newr2 = row + diffr;
+                const newc2 = col + diffc;
+                if (newr2 < width and newc2 >= 0 and newc2 < width and !distinct[@intCast(newr2)][@intCast(newc2)]) {
+                    distinct[@intCast(newr2)][@intCast(newc2)] = true;
+                    total_distinct += 1;
+                }
+            }
+
+            try lookup[item].append(.{ row, col });
+            col += 1;
+        }
+    }
+
+    print("{d}\n", .{total_distinct});
+}
+
+fn part2(lookup: *[256]std.ArrayList(std.meta.Tuple(&.{ i32, i32 })), distinct: [][]bool, lines: *std.mem.SplitIterator(u8, .scalar), width: usize) !void {
+    var row: i32 = 0;
+    var total_distinct: usize = 0;
+    while (lines.next()) |line| : (row += 1) {
+        if (line.len == 0) break;
+
+        var col: i32 = 0;
+        for (line) |item| {
+            if (item == '.' or item == '#') {
+                col += 1;
+                continue;
+            }
+
+            for (lookup[item].items) |antenna| {
+                const diffr = row - antenna[0];
+                const diffc = col - antenna[1];
+
+                var newr1 = antenna[0];
+                var newc1 = antenna[1];
+                while (newr1 >= 0 and newc1 >= 0 and newc1 < width) {
+                    if (!distinct[@intCast(newr1)][@intCast(newc1)]) {
+                        distinct[@intCast(newr1)][@intCast(newc1)] = true;
+                        total_distinct += 1;
+                    }
+                    newr1 -= diffr;
+                    newc1 -= diffc;
+                }
+
+                var newr2 = row;
+                var newc2 = col;
+                while (newr2 < width and newc2 >= 0 and newc2 < width) {
+                    if (!distinct[@intCast(newr2)][@intCast(newc2)]) {
+                        distinct[@intCast(newr2)][@intCast(newc2)] = true;
+                        total_distinct += 1;
+                    }
+                    newr2 += diffr;
+                    newc2 += diffc;
+                }
+            }
+
+            try lookup[item].append(.{ row, col });
+            col += 1;
+        }
+    }
+
+    print("{d}\n", .{total_distinct});
+}