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use structopt::StructOpt;
#[derive(Debug, StructOpt)]
#[structopt(name = "Day 4: Secure Container")]
/// Calculates how many possible lock values there are
///
/// See https://adventofcode.com/2019/day/4 for details.
struct Opt {
/// Repeated digits must be exactly 2 long
#[structopt(long = "larger-range-rule")]
larger_range_rule: bool,
min: u32,
max: u32,
}
fn main() {
let opt = Opt::from_args();
println!(
"{}",
valid_combinations(opt.min, opt.max, opt.larger_range_rule)
)
}
fn valid_combinations(min: u32, max: u32, larger_range_rule: bool) -> u32 {
(min..max)
.filter(|x| {
two_adjacent_identical_digits(*x, larger_range_rule) && digits_never_decrease(*x)
})
.count() as u32
}
fn two_adjacent_identical_digits(x: u32, larger_range_rule: bool) -> bool {
if larger_range_rule {
(0..5).any(|d| {
digit(x, d) == digit(x, d + 1)
&& digit(x, d) != digit(x, d + 2)
&& digit(x, d) != digit(x, d - 1)
})
} else {
(0..5).any(|d| digit(x, d) == digit(x, d + 1))
}
}
fn digits_never_decrease(x: u32) -> bool {
(0..5).all(|d| digit(x, d) >= digit(x, d + 1))
}
fn digit(x: u32, digit: i32) -> u32 {
if digit < 0 {
0
} else {
(x / 10u32.pow(digit as u32)) % 10
}
}
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