102 lines
2.0 KiB
Rust
102 lines
2.0 KiB
Rust
fn is_safe(l: char, c: char, r: char) -> bool {
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// Rule #1.
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if l == '^' && c == '^' && r == '.' {
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return false;
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}
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// Rule #2.
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if l == '.' && c == '^' && r == '^' {
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return false;
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}
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// Rule #3.
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if l == '^' && c == '.' && r == '.' {
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return false;
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}
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// Rule #4.
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if l == '.' && c == '.' && r == '^' {
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return false;
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}
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true
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}
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pub fn evaluate(input: &str) -> String {
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let input = input.chars().collect::<Vec<char>>();
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let mut output = String::new();
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for i in 0..input.len() {
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let c = if i == 0 {
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if is_safe('.', input[i], input[i + 1]) {
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'.'
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} else {
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'^'
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}
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} else if i == input.len() - 1 {
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if is_safe(input[i - 1], input[i], '.') {
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'.'
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} else {
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'^'
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}
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} else {
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if is_safe(input[i - 1], input[i], input[i + 1]) {
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'.'
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} else {
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'^'
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}
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};
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output.push(c);
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}
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output
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}
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fn main() {
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let mut map = Vec::new();
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map.push(".^^^^^.^^.^^^.^...^..^^.^.^..^^^^^^^^^^..^...^^.^..^^^^..^^^^...^.^.^^^^^^^^....^..^^^^^^.^^^.^^^.^^".to_owned());
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while map.len() < 400000 {
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let next = {
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let last = map.last().unwrap();
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evaluate(last)
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};
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map.push(next);
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}
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let count: usize = map.iter()
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.map(|row| {
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row.chars()
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.filter(|c| *c == '.')
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.count()
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})
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.sum();
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println!("safe_tiles={}", count);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn example_01() {
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assert_eq!(".^^^^".to_owned(), evaluate("..^^."));
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}
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#[test]
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fn example_02() {
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assert_eq!("^^..^".to_owned(), evaluate(".^^^^"));
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}
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#[test]
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fn example_03() {
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assert_eq!("^^^...^..^".to_owned(), evaluate(".^^.^.^^^^"));
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}
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}
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