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fn cycle(input: &mut Vec<Vec<char>>) {
let mut sl: usize;
// north
for j in 0..input[0].len() {
sl = 0;
for i in 0..input.len() {
if input[i][j] == 'O' {
if sl != i {
input[sl][j] = 'O';
input[i][j] = '.';
}
sl += 1;
} else if input[i][j] == '#' {
sl = i + 1;
}
}
}
// west
for i in 0..input.len() {
sl = 0;
for j in 0..input[0].len() {
if input[i][j] == 'O' {
if sl != j {
input[i][sl] = 'O';
input[i][j] = '.';
}
sl += 1;
} else if input[i][j] == '#' {
sl = j + 1;
}
}
}
// south
for j in 0..input[0].len() {
sl = input.len() - 1;
for i in (0..input.len()).rev() {
if input[i][j] == 'O' {
if sl != i {
input[sl][j] = 'O';
input[i][j] = '.';
}
if i != 0 {
sl -= 1;
}
} else if input[i][j] == '#' {
if i != 0 {
sl = i - 1;
}
}
}
}
// east
for i in 0..input.len() {
sl = input[0].len() - 1;
for j in (0..input[0].len()).rev() {
if input[i][j] == 'O' {
if sl != j {
input[i][sl] = 'O';
input[i][j] = '.';
}
if j != 0 {
sl -= 1;
}
} else if input[i][j] == '#' {
if j != 0 {
sl = j - 1;
}
}
}
}
}
fn sum(input: &Vec<Vec<char>>) -> u64 {
let mut sum: u64 = 0;
for i in 0..input.len() {
for j in 0..input[0].len() {
if input[i][j] == 'O' {
sum += (input.len() - i) as u64;
}
}
}
return sum;
}
fn cycle_len(a: &Vec<u64>) -> u64 {
for cl in 2..(a.len() / 3) {
let mut ind = true;
for i in 0..cl {
if a[i] != a[cl + i] || a[cl + i] != a[cl * 2 + i] {
ind = false;
break;
}
}
if ind {
return cl as u64;
}
}
return 0;
}
pub fn main() {
let txt = std::fs::read_to_string("./input/day14.txt").unwrap();
let mut input = txt
.lines()
.map(|s| s.chars().collect::<Vec<char>>())
.collect::<Vec<Vec<char>>>();
let mut a = vec![];
for i in 0..1000 {
cycle(&mut input);
if i > 500 {
a.push(sum(&input));
}
}
let cl = cycle_len(&a);
assert_ne!(cl, 0);
let c = 1000000000 - 501 - 1;
println!("{}", a[(c % cl) as usize]);
}
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