5 files changed, 964 insertions, 0 deletions

diff --git a/src/12/input b/src/12/input
new file mode 100644
index 0000000..987fe92
--- /dev/null
+++ b/src/12/input
@@ -0,0 +1,786 @@
+L90
+F67
+R270
+W1
+R180
+F5
+E5
+F59
+E4
+L180
+F70
+S2
+F35
+N3
+E5
+F58
+L90
+N1
+F46
+R90
+S1
+R90
+E1
+L180
+W4
+F99
+N2
+F84
+N1
+R90
+N5
+W4
+F26
+E1
+F97
+N1
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+W1
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+S4
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+R90
+E4
+F14
+R90
+S2
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+S3
+F21
+N1
+W4
+S4
+E1
+L180
+N5
+F30
+N3
+F4
+N5
+F100
+N2
+R270
+E1
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+L90
+W5
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+E2
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+L90
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diff --git a/src/12/input-test b/src/12/input-test
new file mode 100644
index 0000000..d382291
--- /dev/null
+++ b/src/12/input-test
@@ -0,0 +1,5 @@
+F10
+N3
+F7
+R90
+F11
diff --git a/src/12/main.zig b/src/12/main.zig
new file mode 100644
index 0000000..12fd5f0
--- /dev/null
+++ b/src/12/main.zig
@@ -0,0 +1,67 @@
+const std = @import("std");
+const aoc = @import("aoc");
+const Pos = aoc.Pos;
+const Dir = aoc.Dir;
+
+const Ship = struct { pos: Pos, waypoint: Pos, dir: usize };
+
+fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var ship = Ship{ .pos = Pos{ .x = 0, .y = 0 }, .waypoint = Pos{ .x = 0, .y = 0 }, .dir = 0 };
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    while (lineit.next()) |line| {
+        const val = try std.fmt.parseInt(u32, line[1..], 10);
+        switch (line[0]) {
+            'N' => ship.pos = ship.pos.add(Dir.North.mult(val)),
+            'S' => ship.pos = ship.pos.add(Dir.South.mult(val)),
+            'E' => ship.pos = ship.pos.add(Dir.East.mult(val)),
+            'W' => ship.pos = ship.pos.add(Dir.West.mult(val)),
+            'L' => ship.dir = Dir.nextCCW(ship.dir, @divExact(val, 90)),
+            'R' => ship.dir = Dir.nextCW(ship.dir, @divExact(val, 90)),
+            'F' => ship.pos = ship.pos.add(Dir.dirs[ship.dir].mult(val)),
+            else => {
+                return aoc.Error.InvalidInput;
+            },
+        }
+    }
+
+    const answer = std.math.absCast(ship.pos.x) + std.math.absCast(ship.pos.y);
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
+}
+
+fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var ship = Ship{ .pos = Pos{ .x = 0, .y = 0 }, .waypoint = Pos{ .x = 10, .y = 1 }, .dir = 0 };
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    while (lineit.next()) |line| {
+        const val = try std.fmt.parseInt(u32, line[1..], 10);
+        switch (line[0]) {
+            'N' => ship.waypoint = ship.waypoint.add(Dir.North.mult(val)),
+            'S' => ship.waypoint = ship.waypoint.add(Dir.South.mult(val)),
+            'E' => ship.waypoint = ship.waypoint.add(Dir.East.mult(val)),
+            'W' => ship.waypoint = ship.waypoint.add(Dir.West.mult(val)),
+            'L' => {
+                var new = Dir.rotCCW(ship.waypoint, @divExact(val, 90));
+                ship.waypoint = new;
+            },
+            'R' => {
+                var new = Dir.rotCW(ship.waypoint, @divExact(val, 90));
+                ship.waypoint = new;
+            },
+            'F' => ship.pos = ship.pos.add(ship.waypoint.mult(val)),
+            else => {
+                return aoc.Error.InvalidInput;
+            },
+        }
+        aoc.debugfmt("{s} {} {} {} {}\n", .{ line, ship.waypoint.x, ship.waypoint.y, ship.pos.x, ship.pos.y });
+    }
+
+    const answer = std.math.absCast(ship.pos.x) + std.math.absCast(ship.pos.y);
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{answer});
+}
+
+pub const main = aoc.main(part1, part2, .{ "1191", "61053" });
diff --git a/src/12/part1 b/src/12/part1
new file mode 100644
index 0000000..831d3c8
--- /dev/null
+++ b/src/12/part1
@@ -0,0 +1,57 @@
+--- Day 12: Rain Risk ---
+
+Your ferry made decent progress toward the island, but the storm came in faster than anyone
+expected. The ferry needs to take evasive actions!
+
+Unfortunately, the ship's navigation computer seems to be malfunctioning; rather than giving a route
+directly to safety, it produced extremely circuitous instructions. When the captain uses the PA
+system to ask if anyone can help, you quickly volunteer.
+
+The navigation instructions (your puzzle input) consists of a sequence of single-character
+actions paired with integer input values. After staring at them for a few
+minutes, you work out what they probably mean:
+
+
+ - Action N means to move north by the given value.
+ - Action S means to move south by the given value.
+ - Action E means to move east by the given value.
+ - Action W means to move west by the given value.
+ - Action L means to turn left the given number of degrees.
+ - Action R means to turn right the given number of degrees.
+ - Action F means to move forward by the given value in the direction the
+ship is currently facing.
+
+
+The ship starts by facing east. Only the L and R actions change the direction the ship
+is facing. (That is, if the ship is facing east and the next instruction is N10, the ship would move
+north 10 units, but would still move east if the following action were F.)
+
+For example:
+
+F10
+N3
+F7
+R90
+F11
+
+These instructions would be handled as follows:
+
+
+ - F10 would move the ship 10 units east (because the ship starts by facing east) to east
+10, north 0.
+ - N3 would move the ship 3 units north to east 10, north 3.
+ - F7 would move the ship another 7 units east (because the ship is still facing east) to
+east 17, north 3.
+ - R90 would cause the ship to turn right by 90 degrees and face south; it remains at
+east 17, north 3.
+ - F11 would move the ship 11 units south to east 17, south 8.
+
+
+At the end of these instructions, the ship's Manhattan distance (sum of the absolute values of its
+east/west position and its north/south position) from its starting position is 17 + 8 =
+25.
+
+Figure out where the navigation instructions lead. What is the Manhattan distance between
+that location and the ship's starting position?
+
+
diff --git a/src/12/part2 b/src/12/part2
new file mode 100644
index 0000000..74d86c0
--- /dev/null
+++ b/src/12/part2
@@ -0,0 +1,49 @@
+--- Part Two ---
+
+Before you can give the destination to the captain, you realize that the actual action meanings were
+printed on the back of the instructions the whole time.
+
+Almost all of the actions indicate how to move a waypoint which is relative to the
+ship's position:
+
+
+ - Action N means to move the waypoint north by the given value.
+ - Action S means to move the waypoint south by the given value.
+ - Action E means to move the waypoint east by the given value.
+ - Action W means to move the waypoint west by the given value.
+ - Action L means to rotate the waypoint around the ship left
+(counter-clockwise) the given number of degrees.
+ - Action R means to rotate the waypoint around the ship right
+(clockwise) the given number of degrees.
+ - Action F means to move forward to the waypoint a number of times equal
+to the given value.
+
+
+The waypoint starts 10 units east and 1 unit north relative to the ship. The waypoint
+is relative to the ship; that is, if the ship moves, the waypoint moves with it.
+
+For example, using the same instructions as above:
+
+
+ - F10 moves the ship to the waypoint 10 times (a total of 100 units east and 10 units
+north), leaving the ship at east 100, north 10. The waypoint stays 10 units east
+and 1 unit north of the ship.
+ - N3 moves the waypoint 3 units north to 10 units east and 4 units north of the ship.
+The ship remains at east 100, north 10.
+ - F7 moves the ship to the waypoint 7 times (a total of 70 units east and 28 units
+north), leaving the ship at east 170, north 38. The waypoint stays 10 units east
+and 4 units north of the ship.
+ - R90 rotates the waypoint around the ship clockwise 90 degrees, moving it to 4 units east
+and 10 units south of the ship. The ship remains at east 170, north 38.
+ - F11 moves the ship to the waypoint 11 times (a total of 44 units east and 110 units
+south), leaving the ship at east 214, south 72. The waypoint stays 4 units east and
+10 units south of the ship.
+
+
+After these operations, the ship's Manhattan distance from its starting position is 214 + 72 =
+286.
+
+Figure out where the navigation instructions actually lead. What is the Manhattan distance
+between that location and the ship's starting position?
+
+