Day4

2025-12-04 19:10:35 +01:00
parent 1b672a9bf5
commit 8110d07313
3 changed files with 262 additions and 0 deletions
--- a/day4/zig/main.zig
+++ b/day4/zig/main.zig
@@ -0,0 +1,113 @@
+const std = @import("std");
+
+const Tile = enum { empty, paper };
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+
+    var stdin_buffer: [1024]u8 = undefined;
+    var stdin_reader = std.fs.File.stdin().reader(&stdin_buffer);
+
+    const stdin = &stdin_reader.interface;
+
+    const allocator = gpa.allocator();
+    var rows = try std.ArrayList(std.ArrayList(Tile)).initCapacity(allocator, 1);
+    defer rows.deinit(allocator);
+
+    while (try stdin.takeDelimiter('\n')) |line| {
+        var row = try std.ArrayList(Tile).initCapacity(allocator, 1);
+        for (line) |c| {
+            switch (c) {
+                '.' => {
+                    try row.append(allocator, Tile.empty);
+                },
+                '@' => {
+                    try row.append(allocator, Tile.paper);
+                },
+                else => unreachable,
+            }
+        }
+        try rows.append(allocator, row);
+    }
+
+    var task1: usize = 0;
+
+    var i: isize = 0;
+    while (i < rows.items.len) : (i += 1) {
+        var j: isize = 0;
+        while (j < rows.items[0].items.len) : (j += 1) {
+            const i_u: usize = @intCast(i);
+            const j_u: usize = @intCast(j);
+            if (rows.items[i_u].items[j_u] != Tile.paper) {
+                continue;
+            }
+
+            const paper_count = countNeighbors(j, i, rows);
+
+            if (paper_count < 4) {
+                task1 += 1;
+            }
+        }
+    }
+
+    var removed_count: usize = 1;
+    var task2: usize = 0;
+
+    while (removed_count > 0) {
+        removed_count = 0;
+        var ii: isize = 0;
+        while (ii < rows.items.len) : (ii += 1) {
+            var j: isize = 0;
+            while (j < rows.items[0].items.len) : (j += 1) {
+                const i_u: usize = @intCast(ii);
+                const j_u: usize = @intCast(j);
+                if (rows.items[i_u].items[j_u] != Tile.paper) {
+                    continue;
+                }
+
+                const paper_count = countNeighbors(j, ii, rows);
+
+                if (paper_count < 4) {
+                    task2 += 1;
+                    rows.items[i_u].items[j_u] = Tile.empty;
+                    removed_count += 1;
+                }
+            }
+        }
+    }
+
+    for (rows.items) |*row| {
+        row.deinit(allocator);
+    }
+
+    std.debug.print("{d}\n", .{task1});
+    std.debug.print("{d}\n", .{task2});
+}
+
+fn countNeighbors(x: isize, y: isize, rows: std.ArrayList(std.ArrayList(Tile))) usize {
+    var paper_count: usize = 0;
+    var i: isize = -1;
+    while (i < 2) : (i += 1) {
+        var j: isize = -1;
+        while (j < 2) : (j += 1) {
+            if (i == 0 and j == 0) {
+                continue;
+            }
+            const x_new = x + i;
+            const y_new = y + j;
+
+            if (x_new < 0 or x_new >= rows.items[0].items.len or y_new < 0 or y_new >= rows.items.len) {
+                continue;
+            }
+
+            const y_new_u: usize = @intCast(y_new);
+            const z_new_u: usize = @intCast(x_new);
+            if (rows.items[y_new_u].items[z_new_u] == Tile.paper) {
+                paper_count += 1;
+            }
+        }
+    }
+
+    return paper_count;
+}