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138 lines
2.3 KiB
138 lines
2.3 KiB
# 计算性能优化
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https://www.reddit.com/r/rust/comments/rn7ozz/find_perfect_number_comparison_go_java_rust/
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```go
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package main
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import (
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"fmt"
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"math"
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"time"
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)
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func main() {
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n := 320000
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nums := make(map[int][]int)
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start := time.Now()
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calPerfs(n, nums)
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fmt.Printf("runtime: %s\n", time.Since(start))
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}
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func calPerfs(n int, nums map[int][]int) {
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for i := 1; i <= n; i++ {
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d := divs(i)
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if sum(d) == i {
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nums[i] = all(d)
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}
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}
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}
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func divs(num int) map[int]struct{} {
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r := make(map[int]struct{})
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r[1] = struct{}{}
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mid := int(math.Sqrt(float64(num)))
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for i := 2; i <= mid; i++ {
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if num%i == 0 {
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r[i] = struct{}{}
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r[num/i] = struct{}{}
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}
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}
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return r
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}
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func sum(ds map[int]struct{}) int {
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var n int
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for k := range ds {
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n += k
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}
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return n
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}
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func all(ds map[int]struct{}) []int {
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var a []int
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for k := range ds {
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a = append(a, k)
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}
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return a
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}
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```
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## 120ms
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```rust
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use std::time::Instant;
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const N: usize = 320_000 ;
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fn is_perfect(n: usize) -> bool {
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//println!("{:?}", n);
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let mut sum = 1;
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let end = (n as f64).sqrt() as usize;
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for i in 2..end + 1{
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if n % i == 0 {
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if i * i == n {
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sum += i;
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}
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else {
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sum += i + n / i;
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}
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}
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}
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sum == n
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}
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fn find_perfs(n: usize) -> Vec<usize> {
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let mut perfs:Vec<usize> = vec![];
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for i in 2..n + 1 {
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if is_perfect(i) {
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perfs.push(i)
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}
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}
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perfs
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}
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fn main() {
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let start = Instant::now();
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let perfects = find_perfs(N);
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println!("{:?}", start.elapsed());
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println!("{:?}, in {:?}", perfects, N);
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}
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```
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## 90ms
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```rust
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use {
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std::{time::Instant},
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};
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const N: usize = 320000;
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// Optimized, takes about 320ms on an Core i7 6700 @ 3.4GHz
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fn cal_perfs2(n: usize) -> Vec<usize> {
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(1..=n)
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.into_iter()
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.filter(|i| cal2(*i) == *i)
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.collect::<Vec<_>>()
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}
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fn cal2(n: usize) -> usize {
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(2..=(n as f64).sqrt() as usize)
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.into_iter()
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.filter_map(|i| if n % i == 0 { Some([i, n / i]) } else { None })
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.map(|a| a[0] + a[1])
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.sum::<usize>()
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+ 1
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}
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fn main() {
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let start = Instant::now();
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let perf2 = cal_perfs2(N);
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println!("{:?}",perf2);
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println!("Optimized: {:?}", start.elapsed());
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}
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``` |