feat(23-day14)

AdventOfCode2023/src/day14/day14.zig

@@ -1,3 +1,172 @@
-pub fn solve(input: [][]const u8) !void {
-    _ = input;
+const std = @import("std");
+const print = std.debug.print;
+
+const ROCK = 'O';
+const OBSTACLE = '#';
+const EMPTY = '.';
+
+const Direction = enum { north, west, south, east };
+
+fn get_direction_offsets(direction: Direction) struct { i32, i32 } {
+    const offsets: struct { i32, i32 } = switch (direction) {
+        Direction.north => .{ -1, 0 },
+        Direction.west => .{ 0, -1 },
+        Direction.south => .{ 1, 0 },
+        Direction.east => .{ 0, 1 },
+    };
+
+    return offsets;
+}
+
+fn print_grid(grid: [][]const u8) void {
+    for (0..grid.len) |i| {
+        for (0..grid[0].len) |j| {
+            print("{c}", .{grid[i][j]});
+        }
+        print("\n", .{});
+    }
+}
+
+fn get_load(grid: [][]const u8) usize {
+    var load: usize = 0;
+
+    for (0..grid.len) |i| {
+        for (0..grid[0].len) |j| {
+            if (grid[i][j] != ROCK) {
+                continue;
+            }
+
+            load += grid.len - i;
+        }
+    }
+
+    return load;
+}
+
+fn stringify_grid(allocator: std.mem.Allocator, grid: [][]const u8) ![]u8 {
+    var length: usize = 0;
+    const row_length = grid[0].len;
+
+    for (0..grid.len) |i| {
+        length += grid[i].len;
+    }
+
+    var stringified = try allocator.alloc(u8, length);
+    for (0..grid.len) |i| {
+        for (0..grid[0].len) |j| {
+            stringified[i * row_length + j] = grid[i][j];
+        }
+    }
+
+    return stringified;
+}
+
+fn rotate_grid(grid_pointer: *[][]u8, direction: Direction) void {
+    const grid = grid_pointer.*;
+    const direction_offset = get_direction_offsets(direction);
+
+    const forI: i32 = direction_offset[0];
+    const forJ: i32 = direction_offset[1];
+
+    while (true) {
+        var has_changed = false;
+
+        for (0..grid.len) |i| {
+            if (direction == Direction.north and i == 0) {
+                continue;
+            }
+
+            if (direction == Direction.south and i == grid.len - 1) {
+                continue;
+            }
+
+            for (0..grid[0].len) |j| {
+                if (direction == Direction.west and j == 0) {
+                    continue;
+                }
+
+                if (direction == Direction.east and j == grid[0].len - 1) {
+                    continue;
+                }
+
+                const current_block = grid[i][j];
+                if (current_block != ROCK) {
+                    continue;
+                }
+
+                const signedI: i32 = @intCast(i);
+                const signedJ: i32 = @intCast(j);
+
+                const offsetI: usize = @intCast(signedI + forI);
+                const offsetJ: usize = @intCast(signedJ + forJ);
+
+                const next_block = grid[offsetI][offsetJ];
+                if (next_block != EMPTY) {
+                    continue;
+                }
+
+                has_changed = true;
+                grid[offsetI][offsetJ] = ROCK;
+                grid[i][j] = EMPTY;
+            }
+        }
+
+        if (!has_changed) {
+            break;
+        }
+    }
+}
+
+const SPINS = 1000000000 * 4;
+
+pub fn solve(input: [][]const u8) !void {
+    var allocator = std.heap.page_allocator;
+
+    var copied_input = try allocator.alloc([]u8, input.len);
+    defer allocator.free(copied_input);
+
+    for (0..copied_input.len) |i| {
+        copied_input[i] = try allocator.alloc(u8, input[0].len);
+        std.mem.copyForwards(u8, copied_input[i], input[i]);
+    }
+
+    var string_set = std.StringHashMap(usize).init(allocator);
+
+    var current_spin: usize = 0;
+
+    while (current_spin < SPINS) {
+        const direction = switch (current_spin % 4) {
+            0 => Direction.north,
+            1 => Direction.west,
+            2 => Direction.south,
+            3 => Direction.east,
+            else => unreachable,
+        };
+
+        rotate_grid(&copied_input, direction);
+        if (direction != Direction.north) {
+            current_spin += 1;
+            continue;
+        }
+
+        const mask = try stringify_grid(allocator, copied_input);
+
+        if (string_set.get(mask)) |last_found| {
+            const cycle = current_spin - last_found;
+            const cycles_to_add = (SPINS - current_spin) / cycle;
+            const fast_forward = cycle * cycles_to_add;
+
+            current_spin += fast_forward;
+
+            if (current_spin > SPINS) {
+                unreachable;
+            }
+        } else {
+            try string_set.put(mask, current_spin);
+        }
+
+        current_spin += 1;
+    }
+
+    print("Part 2: {}\n", .{get_load(copied_input)});
 }

AdventOfCode2023/src/main.zig

@@ -10,8 +10,8 @@ const std = @import("std");
 // const day10 = @import("./day10/day10.zig");
 // const day11 = @import("./day11/day11.zig");
 // const day = @import("./day12/day12.zig");
-// const day14 = @import("./day14/day14.zig");
-const day13 = @import("./day13/day13.zig");
+const day14 = @import("./day14/day14.zig");
+// const day13 = @import("./day13/day13.zig");
 // const day15 = @import("./day15/day15.zig");
 // const day16 = @import("./day16/day16.zig");
 // const day18 = @import("./day18/day18.zig");
@@ -23,8 +23,8 @@ const utils = @import("utils.zig");
 
 pub fn main() !void {
     const allocator = std.heap.page_allocator;
-    var input = try utils.getInput("./src/day13/input.txt", allocator);
+    const input = try utils.getInput("./src/day14/input.txt", allocator);
     defer allocator.free(input);
 
-    try day13.solve(input);
+    try day14.solve(input);
 }

AdventOfCode2023/src/utils.zig

@@ -4,7 +4,7 @@ const ArrayList = std.ArrayList;
 
 pub fn getInput(fileName: []const u8, allocator: mem.Allocator) !([][]u8) {
     const file = try std.fs.cwd().openFile(fileName, .{});
-    var content = try file.reader().readAllAlloc(allocator, 999999);
+    const content = try file.reader().readAllAlloc(allocator, 999999);
 
     var lines = ArrayList([]u8).init(allocator);
     defer lines.deinit();
@@ -12,13 +12,13 @@ pub fn getInput(fileName: []const u8, allocator: mem.Allocator) !([][]u8) {
     var iterator = mem.split(u8, content, "\n");
 
     while (iterator.next()) |line| {
-        var mutableSlice = try allocator.alloc(u8, line.len);
-        std.mem.copy(u8, mutableSlice, line);
+        const mutableSlice = try allocator.alloc(u8, line.len);
+        std.mem.copyForwards(u8, mutableSlice, line);
 
         try lines.append(mutableSlice);
     }
 
-    var input = try lines.toOwnedSlice();
+    const input = try lines.toOwnedSlice();
 
-    return input;
+    return input[0 .. input.len - 1];
 }