aoc/day12/src/main.zig

const std = @import("std");

pub fn main() anyerror!void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    var gpa = &arena.allocator;

    var f = try std.fs.cwd().openFile("input", .{});
    var contents = try f.readToEndAlloc(gpa, std.math.maxInt(u32));
    defer gpa.free(contents);

    var ship = ShipPosition{};
    var it = std.mem.tokenize(contents, "\n");
    while (it.next()) |line| {
        ship.update(line[0], try std.fmt.parseInt(i64, line[1..], 10));
        std.log.debug("After '{}', ship at ({}, {}) facing {}",
                      .{line, ship.position[0], ship.position[1], ship.facing});
    }
    std.log.info("Ship is at ({},{}) facing {}. It has travalled {} manhattan distance from start",
                 .{ship.position[0], ship.position[1], ship.facing,
                   ship.manhattan_distance_from([_]i64{0, 0})});

    // Part 2
    ship = ShipPosition{};
    it = std.mem.tokenize(contents, "\n");
    while (it.next()) |line| {
        ship.update_part2(line[0], try std.fmt.parseInt(i64, line[1..], 10));
        std.log.debug("After '{}', ship at ({}, {}), with waypoint ({}, {})",
                      .{line, ship.position[0], ship.position[1],
                        ship.waypoint[0], ship.waypoint[1]});
    }
    std.log.info("Ship is at ({},{}) facing {} and waypoint ({}, {}). It has travalled {} manhattan distance from start",
                 .{ship.position[0], ship.position[1], ship.facing,
                   ship.waypoint[0], ship.waypoint[1],
                   ship.manhattan_distance_from([_]i64{0, 0})});
}

const ShipPosition = struct {
    facing : i64 = 90,
    position : [2]i64 = [_]i64{0, 0},
    waypoint: [2]i64 = [_]i64{10, 1},

    pub fn update(self: *ShipPosition, command: u8, value: i64) void {
        switch(command) {
            'N' => {
                self.position[1] += value;
            },
            'S' => {
                self.position[1] -= value;
            },
            'E' => {
                self.position[0] += value;
            },
            'W' => {
                self.position[0] -= value;
            },
            'R' => {
                self.facing += value;
            },
            'L' => {
                self.facing -= value;
            },
            'F' => {
                std.log.debug("Facing before moving forward: {}", .{self.facing});
                while (self.facing < 0) {
                    self.facing += 360;
                }
                if (self.facing >= 360) {
                    self.facing = @intCast(i64, @mod(self.facing, 360));
                }
                std.log.debug("Facing after normalizing, before moving forward: {}",
                              .{self.facing});
                var c : u8 = switch(self.facing) {
                    0 => 'N',
                    90 => 'E',
                    180 => 'S',
                    270 => 'W',
                    else => {
                        std.log.warn("Unexpected facing {}", .{self.facing});
                        unreachable;
                    },
                };
                self.update(c, value);
            },
            else => {
                std.log.warn("Unknown command: '{}'", .{command});
            },
        }
    }

    pub fn manhattan_distance_from(self: *ShipPosition, from: [2]i64) u64 {
        return (std.math.absCast(self.position[0] - from[0])) +
            (std.math.absCast(self.position[1] - from [1]));
    }

    pub fn update_part2(self: *ShipPosition, command: u8, value: i64) void {
        switch(command) {
            'N' => {
                self.waypoint[1] += value;
            },
            'S' => {
                self.waypoint[1] -= value;
            },
            'E' => {
                self.waypoint[0] += value;
            },
            'W' => {
                self.waypoint[0] -= value;
            },
            'R' => {
                // Rotate around the ship
                self.waypoint = rotate_point(self.waypoint, -value);
            },
            'L' => {
                // Rotate around the ship
                self.waypoint = rotate_point(self.waypoint, value);
            },
            'F' => {
                // For forward value times towards the waypoint.
                self.position[0] += self.waypoint[0] * value;
                self.position[1] += self.waypoint[1] * value;
                // Waypoint stays relative to ship
                //self.waypoint[0] = self.position[0] + self.waypoint[0];
                //self.waypoint[1] = self.position[1] + self.waypoint[1];
            },
            else => {
                std.log.warn("Unknown command: '{}'", .{command});
            },
        }
    }

};

pub fn rotate_point(point: [2]i64, degrees: i64) [2]i64 {
    var radians : f64 = (@intToFloat(f64, degrees) * std.math.pi) / 180.0;
    var old_x = @intToFloat(f64, point[0]);
    var old_y = @intToFloat(f64, point[1]);
    var x : f64 = old_x * std.math.cos(radians) - old_y * std.math.sin(radians);
    var y : f64 = old_y * std.math.cos(radians) + old_x * std.math.sin(radians);
    return [2]i64 {
        @floatToInt(i64, std.math.round(x)),
        @floatToInt(i64, std.math.round(y)),
    };
}

test "part_one" {
    var data = [_][]const u8 {
        "F10",
        "N3",
        "F7",
        "R90",
        "F11",
    };
    var ship = ShipPosition{};
    for (data) |d| {
        ship.update(d[0], try std.fmt.parseInt(i64, d[1..], 10));
    }
    std.testing.expectEqual(ship.position[0], 17);
    std.testing.expectEqual(ship.position[1], -8);
    std.testing.expectEqual(ship.manhattan_distance_from([_]i64{0, 0}), 25);
}

test "part_two" {
    var data = [_][]const u8 {
        "F10",
        "N3",
        "F7",
        "R90",
        "F11",
    };
    var ship = ShipPosition{};
    for (data) |d| {
        ship.update_part2(d[0], try std.fmt.parseInt(i64, d[1..], 10));
        std.log.warn("After '{}', ship at ({}, {}), with waypoint ({}, {})",
                      .{d, ship.position[0], ship.position[1],
                        ship.waypoint[0], ship.waypoint[1]});
    }
    std.testing.expectEqual(ship.position[0], 214);
    std.testing.expectEqual(ship.position[1], -72);
    std.testing.expectEqual(ship.manhattan_distance_from([_]i64{0, 0}), 286);
}

// test "rotate" {
//     var point = [_]i64 {4,-3};
//     var p = rotate_point(point, 90);
//     std.testing.expectEqual(p[0], 3);
//     std.testing.expectEqual(p[1], 4);

//     p = rotate_point(point, 180);
//     std.testing.expectEqual(p[0], -4);
//     std.testing.expectEqual(p[1], 3);

//     p = rotate_point(point, 270);
//     std.testing.expectEqual(p[0], -4);
//     std.testing.expectEqual(p[1], 3);

// }