advent-of-code/2022/13-distress-signal/first.zig

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2022-12-13 17:41:44 +01:00
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;
}