aoc/year2015/
day21.rs

1//! # RPG Simulator 20XX
2//!
3//! The trick to get the outcome of each battle quickly is to divide the hero's health by the
4//! boss's damage and vice-versa then find out how many turns each takes to win.
5use std::ops::Add;
6
7use crate::util::iter::*;
8use crate::util::parse::*;
9
10type Input = (u32, u32);
11
12#[derive(Clone, Copy)]
13struct Item {
14    cost: u32,
15    damage: u32,
16    armor: u32,
17}
18
19impl Add for Item {
20    type Output = Self;
21
22    fn add(self, rhs: Self) -> Self {
23        Self {
24            cost: self.cost + rhs.cost,
25            damage: self.damage + rhs.damage,
26            armor: self.armor + rhs.armor,
27        }
28    }
29}
30
31pub fn parse(input: &str) -> Input {
32    let [boss_health, boss_damage, boss_armor]: [u32; 3] =
33        input.iter_unsigned().chunk::<3>().next().unwrap();
34
35    let weapon = [
36        Item { cost: 8, damage: 4, armor: 0 },
37        Item { cost: 10, damage: 5, armor: 0 },
38        Item { cost: 25, damage: 6, armor: 0 },
39        Item { cost: 40, damage: 7, armor: 0 },
40        Item { cost: 74, damage: 8, armor: 0 },
41    ];
42
43    let armor = [
44        Item { cost: 0, damage: 0, armor: 0 },
45        Item { cost: 13, damage: 0, armor: 1 },
46        Item { cost: 31, damage: 0, armor: 2 },
47        Item { cost: 53, damage: 0, armor: 3 },
48        Item { cost: 75, damage: 0, armor: 4 },
49        Item { cost: 102, damage: 0, armor: 5 },
50    ];
51
52    let ring = [
53        Item { cost: 25, damage: 1, armor: 0 },
54        Item { cost: 50, damage: 2, armor: 0 },
55        Item { cost: 100, damage: 3, armor: 0 },
56        Item { cost: 20, damage: 0, armor: 1 },
57        Item { cost: 40, damage: 0, armor: 2 },
58        Item { cost: 80, damage: 0, armor: 3 },
59    ];
60
61    let mut combinations = Vec::with_capacity(22);
62    combinations.push(Item { cost: 0, damage: 0, armor: 0 });
63
64    for (i, &first) in ring.iter().enumerate() {
65        combinations.push(first);
66        for &second in &ring[i + 1..] {
67            combinations.push(first + second);
68        }
69    }
70
71    let mut part_one = u32::MAX;
72    let mut part_two = u32::MIN;
73
74    for first in weapon {
75        for second in armor {
76            for &third in &combinations {
77                let Item { cost, damage, armor } = first + second + third;
78
79                let hero_hit = damage.saturating_sub(boss_armor).max(1);
80                let hero_turns = boss_health.div_ceil(hero_hit);
81                let boss_hit = boss_damage.saturating_sub(armor).max(1);
82                let boss_turns = 100_u32.div_ceil(boss_hit);
83
84                if hero_turns <= boss_turns {
85                    part_one = part_one.min(cost);
86                } else {
87                    part_two = part_two.max(cost);
88                }
89            }
90        }
91    }
92
93    (part_one, part_two)
94}
95
96pub fn part1(input: &Input) -> u32 {
97    input.0
98}
99
100pub fn part2(input: &Input) -> u32 {
101    input.1
102}
aoc/year2015/day21.rs

aoc/year2015/
day21.rs
