Finish day04, part 2

src/days/day04.zig

@@ -1,46 +1,77 @@
 const std = @import("std");
 
-pub const title = "Day 04";
+pub const title = "Day 04: Printing Department";
 
 pub fn run(_: std.mem.Allocator) !void {
-    const input = @embedFile("./input/day04.txt");
-    var lines = std.mem.tokenizeScalar(u8, input, '\n');
+    const initial_input = @embedFile("./input/day04.txt");
+    //const initial_input =
+    //    \\..@@.@@@@.
+    //    \\@@@.@.@.@@
+    //    \\@@@@@.@.@@
+    //    \\@.@@@@..@.
+    //    \\@@.@@@@.@@
+    //    \\.@@@@@@@.@
+    //    \\.@.@.@.@@@
+    //    \\@.@@@.@@@@
+    //    \\.@@@@@@@@.
+    //    \\@.@.@@@.@.
+    //    ;
+
+    const input: []u8 = @constCast(initial_input);
 
     var accumulator: u32 = 0;
 
-    var previous_line: ?[]const u8 = null;
-    while (lines.next()) |line| {
-        const next_line = lines.peek();
+    while (true) {
+        std.debug.print("{s}\n", .{input});
 
-        if (previous_line) |p| std.debug.assert(line.len == p.len);
-        if (next_line) |n| std.debug.assert(line.len == n.len);
+        var rolls_removed: u32 = 0;
 
-        for (line, 0..) |c, i| {
-            if (c != '@') continue;
+        var lines = std.mem.tokenizeScalar(u8, input, '\n');
 
-            var rolls: u8 = 0;
+        var previous_line: ?[]const u8 = null;
+        var line_index: usize = 0;
+        while (lines.next()) |line| {
+            const next_line = lines.peek();
 
-            if (previous_line) |p| {
-                if (i > 0 and p[i - 1] == '@') rolls += 1;
-                if (p[i] == '@') rolls += 1;
-                if (i < p.len - 1 and p[i + 1] == '@') rolls += 1;
+            if (previous_line) |p| std.debug.assert(line.len == p.len);
+            if (next_line) |n| std.debug.assert(line.len == n.len);
+
+            for (line, 0..) |c, i| {
+                if (c != '@') continue;
+
+                var rolls: u8 = 0;
+
+                if (previous_line) |p| {
+                    if (i > 0 and p[i - 1] == '@') rolls += 1;
+                    if (p[i] == '@') rolls += 1;
+                    if (i < p.len - 1 and p[i + 1] == '@') rolls += 1;
+                }
+
+                if (i > 0 and line[i - 1] == '@') rolls += 1;
+                if (i < line.len - 1 and line[i + 1] == '@') rolls += 1;
+
+                if (next_line) |n| {
+                    if (i > 0 and n[i - 1] == '@') rolls += 1;
+                    if (n[i] == '@') rolls += 1;
+                    if (i < n.len - 1 and n[i + 1] == '@') rolls += 1;
+                }
+
+                if (rolls < 4) {
+                    input[(line_index * (line.len + 1)) + i] = 'x';
+                    rolls_removed += 1;
+                }
             }
 
-            if (i > 0 and line[i - 1] == '@') rolls += 1;
-            if (i < line.len - 1 and line[i + 1] == '@') rolls += 1;
-
-            if (next_line) |n| {
-                if (i > 0 and n[i - 1] == '@') rolls += 1;
-                if (n[i] == '@') rolls += 1;
-                if (i < n.len - 1 and n[i + 1] == '@') rolls += 1;
-            }
-
-            if (rolls < 4) {
-                accumulator += 1;
-            }
+            previous_line = line;
+            line_index += 1;
         }
 
-        previous_line = line;
+        std.debug.print("removed {d} rolls\n", .{rolls_removed});
+        if (rolls_removed > 0) {
+            accumulator += rolls_removed;
+        } else {
+            break;
+        }
     }
 
     var buffer: [8]u8 = undefined;