2022-13 in zig

2022/13-distress-signal/first.zig

@@ -0,0 +1,155 @@
+const std = @import("std");
+
+const example = @embedFile("example");
+const input = @embedFile("input");
+
+var allocator: std.mem.Allocator = undefined;
+
+pub fn main() anyerror!void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    allocator = arena.allocator();
+
+    try std.testing.expectEqual(try solve(example), 13);
+    const result = try solve(input);
+    try std.io.getStdOut().writer().print("{}\n", .{result});
+}
+
+const ListErrors = error{
+    OutOfMemory,
+};
+
+const List = struct {
+    data: std.ArrayList(Elt),
+    fn init(reader: anytype) !*List {
+        var l = try allocator.create(List);
+        l.data = std.ArrayList(Elt).init(allocator);
+        while (true) {
+            const c = reader.readByte() catch break;
+            switch (c) {
+                '[' => {
+                    var e = try l.data.addOne();
+                    e.* = Elt{ .list = try List.init(reader) };
+                },
+                ']' => {
+                    return l;
+                },
+                ',' => { // comma after a list ending, ignore
+                },
+                else => { // a digit
+                    var e = try l.data.addOne();
+                    e.* = Elt{ .int = c - '0' };
+                    while (true) {
+                        const d = reader.readByte() catch unreachable;
+                        if (d == ']') {
+                            return l;
+                        } else if (d == ',') {
+                            break;
+                        }
+                        e.int = e.int * 10 + d;
+                    }
+                },
+            }
+        }
+        return l;
+    }
+    fn initSingleton(n: u8) !*List {
+        var l = try allocator.create(List);
+        l.data = std.ArrayList(Elt).init(allocator);
+        var e = try l.data.addOne();
+        e.* = Elt{ .int = n };
+        return l;
+    }
+    fn isLowerThan(l: *List, o: *List) ListErrors!?bool {
+        var i: usize = 0;
+        while (true) : (i += 1) {
+            if (o.len() <= i) {
+                if (l.len() <= i) {
+                    return null;
+                }
+                return false;
+            }
+            if (l.len() <= i) {
+                return true;
+            }
+            const t = try l.data.items[i].isLowerThan(&(o.data.items[i]));
+            if (t != null) {
+                return t;
+            }
+        }
+    }
+    inline fn len(l: *List) usize {
+        return l.data.items.len;
+    }
+    fn print(l: *List) void {
+        for (l.data.items) |e| {
+            switch (e) {
+                Elt.int => |i| std.debug.print("{d} ", .{i}),
+                Elt.list => |o| {
+                    std.debug.print("[", .{});
+                    o.print();
+                    std.debug.print("]", .{});
+                },
+            }
+        }
+    }
+};
+
+const EltType = enum {
+    int,
+    list,
+};
+
+const Elt = union(EltType) {
+    int: u8,
+    list: *List,
+    fn isLowerThan(e: *Elt, f: *Elt) !?bool {
+        switch (e.*) {
+            Elt.int => |i| switch (f.*) {
+                Elt.int => |j| {
+                    if (i == j) {
+                        return null;
+                    }
+                    return i < j;
+                },
+                Elt.list => |o| {
+                    var l = try List.initSingleton(i);
+                    return l.isLowerThan(o);
+                },
+            },
+            Elt.list => |l| switch (f.*) {
+                Elt.int => |j| {
+                    f.* = Elt{ .list = try List.initSingleton(j) };
+                    return e.isLowerThan(f);
+                },
+                Elt.list => |o| {
+                    return l.isLowerThan(o);
+                },
+            },
+        }
+    }
+};
+
+fn solve(puzzle: []const u8) !u64 {
+    var it = std.mem.tokenize(u8, puzzle, "\n");
+    var i: usize = 1;
+    var tot: usize = 0;
+    while (it.next()) |line| {
+        var firstLine = std.io.fixedBufferStream(line);
+        var first = try List.init(firstLine.reader());
+        var secondLine = std.io.fixedBufferStream(it.next() orelse unreachable);
+        var second = try List.init(secondLine.reader());
+        const t = try first.isLowerThan(second);
+        //first.print();
+        //std.debug.print("\n", .{});
+        //second.print();
+        //std.debug.print("\n{d}: {?}\n", .{ i, t });
+        if (t) |s| {
+            if (s) {
+                tot += i;
+            }
+        }
+        i += 1;
+    }
+    return tot;
+}