Advent Of Code 2020 - 01

aoc-2020-01.zig

const std = @import("std");
const input = @embedFile("input");

const testing = std.testing;
const expect = testing.expect;
const print = std.debug.print;

pub fn main() anyerror!void {
    var nums = try numberList(std.heap.page_allocator);

    print("Part1: {}\n", .{try part1(nums)});
    print("Part2: {}\n", .{try part2(nums)});
}

pub fn numberList(allocator: *std.mem.Allocator) ![]const u32 {
    var list = std.ArrayList(u32).init(allocator);
    defer list.deinit();

    var it = std.mem.split(input, "\n");

    while (it.next()) |num| {
        try list.append(std.fmt.parseUnsigned(u32, num, 10) catch continue);
    }

    return list.toOwnedSlice();
}

pub fn part1(nums: []const u32) !u64 {
    for (nums) |x, idx0| {
        for (nums[idx0 + 1 ..]) |y, idx1| {
            if ((x + y) == 2020) {
                return x * y;
            }
        }
    }

    return 0;
}

test "part1" {
    const array = [_]u32{
        1721,
        979,
        366,
        299,
        675,
        1456,
    };

    const result = try part1(array[0..]);

    expect(result == 514579);
}

pub fn part2(nums: []const u32) !u64 {
    for (nums) |x, idx0| {
        for (nums[idx0 + 1 ..]) |y, idx1| {
            for (nums[std.math.max(idx0, idx1) + 1 ..]) |z, idx2| {
                if ((x + y + z) == 2020) {
                    return x * y * z;
                }
            }
        }
    }

    return 0;
}

test "part2" {
    const array = [_]u32{
        1721,
        979,
        366,
        299,
        675,
        1456,
    };

    const result = try part2(array[0..]);

    expect(result == 241861950);
}