day 17, part 1 (slow inefficient solution)

day17-easy/build.zig

@@ -0,0 +1,70 @@
+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "day17-easy",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_unit_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_unit_tests.step);
+}

day17-easy/easy.in

@@ -0,0 +1,141 @@
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day17-easy/sample.in

@@ -0,0 +1,13 @@
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+4322674655533

day17-easy/src/main.zig

@@ -0,0 +1,176 @@
+const std = @import("std");
+
+fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
+    return struct {
+        const Self = @This();
+        mem: [capacity]T,
+        length: capacity_type,
+
+        fn add(self: *Self, value: T) void {
+            self.mem[self.length] = value;
+            self.length += 1;
+        }
+
+        fn addIfNotNull(self: *Self, nullable_value: ?T) void {
+            if (nullable_value) |value| {
+                self.add(value);
+            }
+        }
+
+        fn has(self: *Self, needle: T) bool {
+            for (0..self.length) |i| {
+                if (self.mem[i] == needle) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        fn getMutableSlice(self: *Self) []T {
+            return (&self.mem)[0..self.length];
+        }
+
+        fn getSlice(self: *const Self) []const T {
+            return self.mem[0..self.length];
+        }
+
+        fn init() Self {
+            return Self{
+                .mem = undefined,
+                .length = 0,
+            };
+        }
+    };
+}
+
+const Direction = enum(u2) {
+    Up,
+    Down,
+    Left,
+    Right,
+};
+
+const ResultsByDirection = std.EnumArray(Direction, u32);
+const Results = [150][150]ResultsByDirection;
+
+const NextCellCoordinates = StackList([2]usize, usize, 3);
+
+fn fillResults(board: []const []const u8, results: *Results, x: usize, y: usize, entry_direction: Direction, depth: usize) void {
+    //std.debug.print("Solving for {d},{d}, {any}, depth: {d}, total: {d}\n", .{ x, y, entry_direction, depth, results.*[x][y].get(entry_direction) });
+    var previous_cells_list = StackList([2]usize, usize, 3).init();
+    switch (entry_direction) {
+        .Up => {
+            for (1..4) |delta| {
+                if (x + delta < board.len) {
+                    previous_cells_list.add(.{ x + delta, y });
+                }
+            }
+        },
+        .Down => {
+            for (1..4) |delta| {
+                if (x >= delta) {
+                    previous_cells_list.add(.{ x - delta, y });
+                }
+            }
+        },
+        .Left => {
+            for (1..4) |delta| {
+                if (y + delta < board[x].len) {
+                    previous_cells_list.add(.{ x, y + delta });
+                }
+            }
+        },
+        .Right => {
+            for (1..4) |delta| {
+                if (y >= delta) {
+                    previous_cells_list.add(.{ x, y - delta });
+                }
+            }
+        },
+    }
+
+    const previous_directions: [2]Direction = switch (entry_direction) {
+        .Up, .Down => .{ .Left, .Right },
+        .Left, .Right => .{ .Up, .Down },
+    };
+
+    var current_heat = results.*[x][y].get(entry_direction);
+    for (previous_cells_list.getSlice()) |previous_cell| {
+        current_heat += board[previous_cell[0]][previous_cell[1]];
+        for (previous_directions) |direction| {
+            if (results.*[previous_cell[0]][previous_cell[1]].get(direction) > current_heat) {
+                results.*[previous_cell[0]][previous_cell[1]].set(direction, current_heat);
+                fillResults(board, results, previous_cell[0], previous_cell[1], direction, depth + 1);
+            }
+        }
+    }
+}
+
+fn solveLines(lines: [][]u8) usize {
+    var total_max: u32 = 0;
+    for (lines) |line| {
+        for (line) |*char| {
+            char.* = char.* - '0';
+            total_max += char.*;
+        }
+    }
+
+    const x_max = lines.len - 1;
+    const y_max = lines[x_max].len - 1;
+
+    var results: Results = [_][150]ResultsByDirection{[_]ResultsByDirection{ResultsByDirection.initFill(total_max)} ** 150} ** 150;
+    results[x_max][y_max].set(.Down, lines[x_max][y_max]);
+    results[x_max][y_max].set(.Right, lines[x_max][y_max]);
+
+    fillResults(lines, &results, x_max, y_max, .Down, 0);
+    fillResults(lines, &results, x_max, y_max, .Right, 0);
+
+    if (false) {
+        for (0..lines.len) |x| {
+            for (0..lines[x].len) |y| {
+                std.debug.print("{d} ", .{@min(@min(results[x][y].get(.Up), results[x][y].get(.Down)), @min(results[x][y].get(.Left), results[x][y].get(.Right)))});
+            }
+            std.debug.print("\n", .{});
+        }
+    }
+
+    return results[0][0].get(.Down) - lines[0][0];
+}
+
+pub fn solveAll(reader: anytype) !usize {
+    var result: usize = 0;
+    while (true) {
+        var allocator_buffer: [20000]u8 = undefined;
+        var fba = std.heap.FixedBufferAllocator.init(&allocator_buffer);
+        var allocator = fba.allocator();
+
+        var lines = StackList([]u8, usize, 150).init();
+        var empty_line_reached = false;
+
+        var line_buffer: [1000]u8 = undefined;
+        while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
+            if (line.len == 0) {
+                empty_line_reached = true;
+                break;
+            }
+            lines.add(try allocator.dupe(u8, line));
+        }
+
+        result += solveLines(lines.getMutableSlice());
+
+        if (!empty_line_reached) {
+            return result;
+        }
+    }
+}
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+
+    const raw_in = std.io.getStdIn();
+    var buffered_reader = std.io.bufferedReader(raw_in.reader());
+    var reader = buffered_reader.reader();
+    const result = try solveAll(&reader);
+    try stdout.print("{d}\n", .{result});
+}