day x

day6/day6_part1.zig

@@ -0,0 +1,134 @@
+const std = @import("std");
+const in = @embedFile("in");
+
+const Direction = struct {
+    x: i32,
+    y: i32,
+
+    const Left = Direction{ .x = -1, .y = 0 };
+    const Right = Direction{ .x = 1, .y = 0 };
+    const Up = Direction{ .x = 0, .y = -1 };
+    const Down = Direction{ .x = 0, .y = 1 };
+
+    pub fn eql(self: Direction, other: Direction) bool {
+        return self.x == other.x and self.y == other.y;
+    }
+};
+
+fn array_includes(comptime T: type, haystack: []T, needle: T) bool {
+    for (haystack) |item| {
+        if (item == needle) {
+            return true;
+        }
+    }
+    return false;
+}
+
+fn turn_right(direction: Direction) Direction {
+    if (direction.eql(Direction.Up)) {
+        return Direction.Right;
+    } else if (direction.eql(Direction.Right)) {
+        return Direction.Down;
+    } else if (direction.eql(Direction.Down)) {
+        return Direction.Left;
+    } else if (direction.eql(Direction.Left)) {
+        return Direction.Up;
+    }
+    unreachable;
+}
+
+fn find_guard(lines: std.ArrayList(std.ArrayList(i8))) [2]i32 {
+    for (lines.items, 0..) |line, y| {
+        for (line.items, 0..) |item, x| {
+            if (item == 1) {
+                return .{ @intCast(x), @intCast(y) };
+            }
+        }
+    }
+    unreachable;
+}
+
+fn print_lines(lines: std.ArrayList(std.ArrayList(i8))) void {
+    for (lines.items) |line| {
+        for (line.items) |item| {
+            switch (item) {
+                -1 => std.debug.print("#", .{}),
+                0 => std.debug.print(".", .{}),
+                1 => std.debug.print("^", .{}),
+                2 => std.debug.print("V", .{}),
+                else => std.debug.print(" ", .{}),
+            }
+        }
+        std.debug.print("\n", .{});
+    }
+}
+
+fn count_visited(lines: std.ArrayList(std.ArrayList(i8))) u32 {
+    var count: u32 = 0;
+    for (lines.items) |line| {
+        for (line.items) |e| {
+            if (e == 2 or e == 1) count += 1;
+        }
+    }
+    return count;
+}
+
+fn move(lines: std.ArrayList(std.ArrayList(i8)), direction: Direction) void {
+    // print_lines(lines);
+    // std.debug.print("\n", .{});
+
+    const pos = find_guard(lines);
+    var x = pos[0];
+    var y = pos[1];
+    lines.items[@intCast(y)].items[@intCast(x)] = 2; // 2 for already visited
+    x += direction.x;
+    y += direction.y;
+
+    if (y < 0 or y >= lines.items.len or x < 0 or x >= lines.items[@intCast(y)].items.len) {
+        return;
+    }
+
+    if (lines.items[@intCast(y)].items[@intCast(x)] == -1) {
+        x -= direction.x;
+        y -= direction.y;
+        lines.items[@intCast(y)].items[@intCast(x)] = 1;
+        return move(lines, turn_right(direction));
+    }
+
+    lines.items[@intCast(y)].items[@intCast(x)] = 1;
+    return move(lines, direction);
+}
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const ally = gpa.allocator();
+    defer _ = gpa.deinit();
+
+    var lines = std.ArrayList(std.ArrayList(i8)).init(ally);
+    defer {
+        for (lines.items) |*line| {
+            line.deinit();
+        }
+        lines.deinit();
+    }
+
+    var in_lines = std.mem.tokenize(u8, in, "\n");
+    while (in_lines.next()) |linestr| {
+        var line = std.ArrayList(i8).init(ally);
+        for (linestr) |c| {
+            const value: i8 = switch (c) {
+                '#' => -1,
+                '.' => 0,
+                '^' => 1,
+                else => -2,
+            };
+            try line.append(value);
+        }
+        try lines.append(line);
+    }
+
+    move(lines, Direction.Up);
+    const moves = count_visited(lines);
+
+    std.debug.print("{d}\n", .{moves});
+}