Created
October 20, 2018 11:34
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use std::time::Instant; | |
use std::collections::VecDeque; | |
fn gcd(a: u32, b: u32) -> u32 { | |
if b != 0 { | |
gcd(b, a % b) | |
} else { | |
a | |
} | |
} | |
fn test_naive(n: u32) -> u32 { | |
let mut ans = 0; | |
for i in 1..n { | |
for j in i+1..n { | |
if gcd(i, j) == 1 && gcd(i, i + j) == 1 && gcd(j, i + j) == 1 { | |
ans += 1; | |
} | |
} | |
} | |
ans | |
} | |
fn f(a: u32, b: u32, n: u32) -> u32 { | |
let mut ans = 0; | |
let mut q = VecDeque::new(); | |
q.push_back((a, b)); | |
while let Some((x, y)) = q.pop_front() { | |
if x < n { | |
if gcd(x, x + y) == 1 && gcd(y, x + y) == 1 { | |
ans += 1; | |
} | |
q.push_back((2 * x - y, x)); | |
q.push_back((2 * x + y, x)); | |
q.push_back((x + 2 * y, y)); | |
} | |
} | |
ans | |
} | |
fn test_smart(n: u32) -> u32 { | |
f(2, 1, n) + f(3, 1, n) | |
} | |
fn main() { | |
let n = 10000; | |
let now = Instant::now(); | |
let res = test_naive(n); | |
println!("test_naive({}) = {}; done in {:?}", n, res, now.elapsed()); | |
let now = Instant::now(); | |
let res = test_smart(n); | |
println!("test_smart({}) = {}; done in {:?}", n, res, now.elapsed()); | |
} |
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