72 lines
1.6 KiB
Plaintext
72 lines
1.6 KiB
Plaintext
fn is_prime(n: u32) -> bool {
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assert!(n < 64);
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((1u64 << n) & 0x28208a20a08a28ac) != 0
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}
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fn prime_triangle_row(a: &mut [u32]) -> bool {
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if a.len() == 2 {
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return is_prime(a[0] + a[1]);
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}
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for i in (1..a.len() - 1).step_by(2) {
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if is_prime(a[0] + a[i]) {
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a.swap(i, 1);
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if prime_triangle_row(&mut a[1..]) {
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return true;
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}
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a.swap(i, 1);
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}
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}
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false
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}
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fn prime_triangle_count(a: &mut [u32]) -> u32 {
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let mut count = 0;
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if a.len() == 2 {
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if is_prime(a[0] + a[1]) {
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count += 1;
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}
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} else {
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for i in (1..a.len() - 1).step_by(2) {
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if is_prime(a[0] + a[i]) {
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a.swap(i, 1);
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count += prime_triangle_count(&mut a[1..]);
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a.swap(i, 1);
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}
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}
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}
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count
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}
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fn print(a: &[u32]) {
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if a.is_empty() {
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return;
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}
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print!("{:2}", a[0]);
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for x in &a[1..] {
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print!(" {:2}", x);
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}
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println!();
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}
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fn main() {
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use std::time::Instant;
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let start = Instant::now();
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for n in 2..21 {
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let mut a: Vec<u32> = (1..=n).collect();
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if prime_triangle_row(&mut a) {
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print(&a);
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}
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}
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println!();
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for n in 2..21 {
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let mut a: Vec<u32> = (1..=n).collect();
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if n > 2 {
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print!(" ");
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}
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print!("{}", prime_triangle_count(&mut a));
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}
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println!();
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let time = start.elapsed();
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println!("\nElapsed time: {} milliseconds", time.as_millis());
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}
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