From 516e6ed4a9066fa43d6159b2a0ec58416ab28013 Mon Sep 17 00:00:00 2001
From: xander <xander@biltopia.org>
Date: Sun, 7 Dec 2025 13:12:06 +0100
Subject: solve up to day 7

---
 src/day04.zig | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 src/day04.zig

(limited to 'src/day04.zig')

diff --git a/src/day04.zig b/src/day04.zig
new file mode 100644
index 0000000..5d7b455
--- /dev/null
+++ b/src/day04.zig
@@ -0,0 +1,99 @@
+const std = @import("std");
+const print = std.debug.print;
+
+pub fn solve(part: []u8, reader: *std.Io.Reader, allocator: std.mem.Allocator) !void {
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(reader, allocator);
+    } else {
+        try part2(reader, allocator);
+    }
+}
+
+
+fn part1(reader: *std.Io.Reader, allocator: std.mem.Allocator) !void {
+    var output: usize = 0;
+    var list = try std.ArrayList([]u8).initCapacity(allocator, 0);
+    defer list.deinit(allocator);
+
+    while (reader.takeDelimiter('\n')) |line| {
+        if (line == null){
+            break;
+        }
+
+        try list.append(allocator, line.?);
+    } else |_| {
+
+    }
+
+
+    for (list.items,0..) |row, y| {
+        for (row,0..) |item,x| {
+            if (item != '@'){
+                continue;
+            }
+
+            var adjacent: usize = 0;
+            if (y > 0 and x > 0 and list.items[y - 1][x - 1] == '@') adjacent += 1;
+            if (y > 0 and list.items[y - 1][x] == '@') adjacent += 1;
+            if (y > 0 and x < row.len - 1 and list.items[y - 1][x + 1] == '@') adjacent += 1;
+            if (x > 0 and list.items[y][x - 1] == '@') adjacent += 1;
+            if (x < row.len - 1 and list.items[y][x + 1] == '@') adjacent += 1;
+            if (y < list.items.len - 1 and x > 0 and list.items[y + 1][x - 1] == '@') adjacent += 1;
+            if (y < list.items.len - 1 and list.items[y + 1][x] == '@') adjacent += 1;
+            if (y < list.items.len - 1 and x < row.len - 1 and list.items[y + 1][x + 1] == '@') adjacent += 1;
+
+            if (adjacent < 4){
+
+                output += 1;
+            }
+        }
+    }
+
+    print("{d}\n", .{output});
+}
+
+fn part2(reader: *std.Io.Reader, allocator: std.mem.Allocator) !void {
+    var output: usize = 0;
+    var list = try std.ArrayList([]u8).initCapacity(allocator, 0);
+    defer list.deinit(allocator);
+
+    while (reader.takeDelimiter('\n')) |line| {
+        if (line == null){
+            break;
+        }
+
+        try list.append(allocator, line.?);
+    } else |_| {
+
+    }
+
+
+    var previous_output: usize = 1;
+    while (output != previous_output) {
+        previous_output = output;
+        for (list.items,0..) |row, y| {
+            for (row,0..) |item,x| {
+                if (item != '@'){
+                    continue;
+                }
+
+                var adjacent: usize = 0;
+                if (y > 0 and x > 0 and list.items[y - 1][x - 1] == '@') adjacent += 1;
+                if (y > 0 and list.items[y - 1][x] == '@') adjacent += 1;
+                if (y > 0 and x < row.len - 1 and list.items[y - 1][x + 1] == '@') adjacent += 1;
+                if (x > 0 and list.items[y][x - 1] == '@') adjacent += 1;
+                if (x < row.len - 1 and list.items[y][x + 1] == '@') adjacent += 1;
+                if (y < list.items.len - 1 and x > 0 and list.items[y + 1][x - 1] == '@') adjacent += 1;
+                if (y < list.items.len - 1 and list.items[y + 1][x] == '@') adjacent += 1;
+                if (y < list.items.len - 1 and x < row.len - 1 and list.items[y + 1][x + 1] == '@') adjacent += 1;
+
+                if (adjacent < 4){
+                    list.items[y][x] = '.';
+                    output += 1;
+                }
+            }
+        }
+    }
+
+    print("{d}\n", .{output});
+}
-- 
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