day10?

src/day10.zig

@@ -0,0 +1,170 @@
+const std = @import("std");
+const util = @import("util.zig");
+const mem = std.mem;
+const assert = std.debug.assert;
+
+pub fn main() !void {
+    const input = @embedFile("data/day10.txt");
+    const sln = try solve(util.gpa, input);
+    try printPipes(std.io.getStdOut(), input);
+    std.debug.print("{d}\n", .{sln.a});
+    std.debug.print("{d}\n", .{sln.b});
+}
+
+const Solution = struct {
+    a: usize,
+    b: usize,
+};
+
+const Direction = enum(u2) {
+    up,
+    down,
+    left,
+    right,
+};
+
+fn Walker(comptime T: type) type {
+    return struct {
+        r: T,
+        c: T,
+        facing: Direction,
+
+        fn init(r: T, c: T) @This() {
+            return .{ .r = r, .c = c, .facing = .up };
+        }
+
+        fn walk(self: *@This(), grid: [][]u8) void {
+            self.walkSpace(grid[self.r][self.c]);
+        }
+
+        fn walkSpace(self: *@This(), char: u8) void {
+            switch (char) {
+                'S' => {},
+                '|' => assert(self.facing == .up or self.facing == .down),
+                '-' => assert(self.facing == .left or self.facing == .right),
+                'L' => switch (self.facing) {
+                    .down => self.turn(.right),
+                    .left => self.turn(.up),
+                    else => unreachable,
+                },
+                'J' => switch (self.facing) {
+                    .down => self.turn(.left),
+                    .right => self.turn(.up),
+                    else => unreachable,
+                },
+                '7' => switch (self.facing) {
+                    .up => self.turn(.left),
+                    .right => self.turn(.down),
+                    else => unreachable,
+                },
+                'F' => switch (self.facing) {
+                    .up => self.turn(.right),
+                    .left => self.turn(.down),
+                    else => unreachable,
+                },
+                else => unreachable,
+            }
+            self.fwd();
+        }
+
+        fn move(self: *@This(), row: i32, col: i32) void {
+            self.*.r += row;
+            self.*.c += col;
+        }
+
+        fn fwd(self: *@This()) void {
+            switch (self.facing) {
+                .up => self.move(-1, 0),
+                .down => self.move(1, 0),
+                .left => self.move(0, -1),
+                .right => self.move(0, 1),
+            }
+        }
+
+        fn turn(self: *@This(), dir: Direction) void {
+            self.*.facing = dir;
+        }
+    };
+}
+
+fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
+    _ = alloc;
+    var grid: [][]u8 = undefined; // try alloc.alloc(u8, mem.count(u8, input, &[_]u8{'\n'}));
+
+    var s_found = false;
+    var sr: u32 = 0;
+    var sc: u32 = 0;
+
+    var it = util.splitLines(input);
+    var curr_row: u32 = 0;
+    while (it.next()) |line| {
+        if (line.len == 0) continue;
+        // grid[curr_row] = line;
+
+        if (!s_found) {
+            if (mem.indexOfScalar(u8, line, 'S')) |col| {
+                _ = col;
+                sr = curr_row;
+                // sc = col;
+                s_found = true;
+            }
+        }
+    }
+
+    // Find actual starting position.
+    var walker = Walker(u32).init(sr, sc);
+    if (mem.indexOfScalar(u8, "|7F", grid[sr - 1][sc])) |_| {
+        walker.facing = .up;
+    } else if (mem.indexOfScalar(u8, "|JL", grid[sr + 1][sc])) |_| {
+        walker.facing = .down;
+    } else if (mem.indexOfScalar(u8, "-LF", grid[sr][sc - 1])) |_| {
+        walker.facing = .left;
+    } else if (mem.indexOfScalar(u8, "-J7", grid[sr][sc + 1])) |_| {
+        walker.facing = .right;
+    }
+
+    var steps: u32 = 1;
+    while (true) {
+        steps += 1;
+        if (grid[walker.r][walker.c] == 'S') break;
+    }
+
+    return .{ .a = steps / 2, .b = 0 };
+}
+
+fn printPipes(writer: anytype, input: []const u8) !void {
+    for (input) |char| {
+        _ = switch (char) {
+            '|' => try writer.write("│"),
+            '-' => try writer.write("─"),
+            'L' => try writer.write("└"),
+            'J' => try writer.write("┘"),
+            '7' => try writer.write("┐"),
+            'F' => try writer.write("┌"),
+            '.' => try writer.write(" "),
+            'S' => try writer.write("o"),
+            '\n' => try writer.write("\n"),
+            else => unreachable,
+        };
+    }
+}
+
+test "silver" {
+    const input =
+        \\-L|F7
+        \\7S-7|
+        \\L|7||
+        \\-L-J|
+        \\L|-JF
+    ;
+    const sln = try solve(std.testing.allocator, input);
+    try std.testing.expectEqual(@as(usize, 6), sln.a);
+}
+
+test "gold" {
+    const input =
+        \\
+    ;
+    const sln = try solve(std.testing.allocator, input);
+    try std.testing.expectEqual(@as(usize, 0), sln.b);
+}