golang notes(7)---PAT (Basic Level) 1007-素數對猜想

Comparison of 'Sieve of Eratosthenes' and 'Sieve of Euler':

refer to:https://www.jianshu.com/p/7867517826e7

Sieve of Eratosthenes (埃氏篩選法）：

func SieveOfEratosthenes(n int) int {
	p := make([]int, 0)
	flagNotPrime := make([]bool, n+1)
	// Sieve of Eratosthenes
	for i := 2; i <= n; i++ {
		if !flagNotPrime[i] {
			p = append(p, i)
			for j := i*i; j <= n; j += i {
				flagNotPrime[j] = true
			}
		}
	}

	return len(p)
}

Sieve of Euler（歐拉篩選法）：

func SieveOfEuler(n int) int {
	p := make([]int, 0)
	flagNotPrime := make([]bool, n+1)
	// Sieve of Eular
	for i := 2; i <= n; i++ {
		if !flagNotPrime[i] {
			p = append(p, i)
		}
		for j := 0; j < len(p) && p[j] * i <= n; j++ {
			flagNotPrime[i*p[j]] = true
			if i % p[j] == 0 {
				break
			}
		}
	}

	return len(p)
}

Here is the benchmarking routines:

package basic_1007_test

import (
	"testing"
	"pta/basic_1007"
)

func BenchmarkSieveOfEratosthenes(b *testing.B) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		basic_1007.SieveOfEratosthenes(100000000)
	}
}

func BenchmarkSieveOfEuler(b *testing.B) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		basic_1007.SieveOfEuler(100000000)
	}
}

Run the benchmarking:

(11:00 dabs@CNU1343VF8 basic_1007) > go test -v -run="none" -bench=. -benchtime="10s" -benchmem
goos: linux
goarch: amd64
pkg: pta/basic_1007
BenchmarkSieveOfEratosthenes
BenchmarkSieveOfEratosthenes-4                10        1048856325 ns/op        370910660 B/op        49 allocs/op
BenchmarkSieveOfEuler
BenchmarkSieveOfEuler-4                        8        1379414530 ns/op        370910476 B/op        49 allocs/op
PASS
ok      pta/basic_1007  23.970s

As we can see, SieveOfEuler is bit slower than SieveOfEratosthenes in golang.

From the OJ of PTA platform:

Run time is 7ms using SieveOfEuler and 5ms using SieveOfEratosthenes.