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static DAY: u8 = 7;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", calibration_result(&input, false));
println!("{DAY}b: {}", calibration_result(&input, true));
}
fn calculateable(result: i64, operands: &[i64], with_concat: bool) -> bool {
if operands.len() == 1 {
return result == operands[0];
}
let rem = &operands[..=operands.len()-2];
let op = operands[operands.len()-1];
if with_concat {
let result_str = result.to_string();
let op_str = op.to_string();
if result_str.ends_with(&op_str) && result_str.len() > op_str.len() {
let result_str = result_str.chars().take(result_str.len() - op_str.len()).collect::<String>();
let result = result_str.parse::<i64>().unwrap();
if calculateable(result, rem, with_concat) {
return true;
}
}
}
((result - op >= 0) && calculateable(result - op, rem, with_concat))
|| (result % op == 0 && calculateable(result / op, rem, with_concat))
}
fn calibration_result(input: &[String], with_concat: bool) -> i64 {
let mut sum = 0;
for line in input {
let (result, operands) = line.split_once(": ").unwrap();
let result = result.parse::<i64>().unwrap();
let operands = operands.split(" ").map(|x| x.parse::<i64>().unwrap()).collect::<Vec<_>>();
if calculateable(result, &operands, with_concat) {
sum += result;
}
}
sum
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"190: 10 19",
"3267: 81 40 27",
"83: 17 5",
"156: 15 6",
"7290: 6 8 6 15",
"161011: 16 10 13",
"192: 17 8 14",
"21037: 9 7 18 13",
"292: 11 6 16 20",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(calibration_result(&input, false), 3749);
assert_eq!(calibration_result(&input, true), 11387);
}
}
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