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JavaScript使用高阶生成器进行过滤以生成素数

作者:42

生成器大家都知道是怎么一回事,但是高阶生成器又是什么东西呢,下面小编就来为大家简单介绍一下如何使用高阶生成器进行过滤以生成素数吧

生成器大家都知道是怎么一回事,但是高阶生成器又是什么东西呢?今天小编就带着大家来一起了解一下吧……

先上代码:

function* numFrom(start: number) {
    while (true) yield start++
}

function* filter(nums: Generator<number>, prime: number) {
    for (const n of nums) if (n % prime !== 0) yield n
}

let cur = numFrom(2)

for (let i = 0; i < 10; i++) {
    const prime = cur.next()
    if (!prime.done) {
        console.log(i, ':', prime.value)
        cur = filter(cur, prime.value)
    }
}

结果:

0 : 2
1 : 3
2 : 5
3 : 7
4 : 11
5 : 13
6 : 17
7 : 19
8 : 23
9 : 29

其中函数 filter 传入一个生成器,返回一个新的生成器,我们可以把它称为高阶生成器。

function* filter(nums: Generator<number>, prime: number) {
    for (const n of nums) if (n % prime !== 0) yield n
}

它的作用是过滤掉 nums: Generator<number> 生成的数中能被 prime 整除的数:

const gen = filter(numFrom(10), 3)
for (let i = 0; i < 10; i++) {
    const n = gen.next()
    if (!n.done) console.log(n.value)
}

结果:

10
11
13
14
16
17
19
20
22
23

可以看到,3 的倍数,12151821 已经被过滤掉了。

如果我们再把函数返回值作为参数传给 filter,就能过滤掉多个值了:

let gen = filter(numFrom(10), 3) // 从 10 开始,不能被 3 整除的数
gen = filter(gen, 5) // 从 10 开始,不能被 3 和 5 整除的数
...

只要我们不断把当前的生成器和产生的素数传入,我们就能够实现过滤,相当于使用筛法生成素数。

let cur = numFrom(2)

for (let i = 0; i < 10; i++) {
    const prime = cur.next()
    if (!prime.done) {
        console.log(i, ':', prime.value)
        cur = filter(cur, prime.value) // 产生新的生成器
    }
}
numFrom(2) -> filter(2) -> filter(3) -> filter(5) -> filter(7) ...

如果还不太清除,可以在控制台打印详细过程:

function* numFrom(start: number) {
    while (true) {
        console.log('\nnum yield', start)
        yield start++
    }
}

let filterDeep = 0
function* filter(nums: Generator<number>, prime: number) {
    const deep = filterDeep++
    for (const n of nums)
        if (n % prime !== 0) {
            console.log(`filter yield[${deep}] ${n}`)
            yield n
        } else console.log(`filtered[${deep}] ${n} by ${prime}`)
}

let cur = numFrom(2)

for (let i = 0; i < 10; i++) {
    const prime = cur.next()
    if (!prime.done) {
        console.log(i, ':', prime.value)
        cur = filter(cur, prime.value)
    }
}

结果:

num yield 2
0 : 2

num yield 3
filter yield[0] 3
1 : 3

num yield 4
filtered[0] 4 by 2

num yield 5
filter yield[0] 5
filter yield[1] 5
2 : 5

num yield 6
filtered[0] 6 by 2

num yield 7
filter yield[0] 7
filter yield[1] 7
filter yield[2] 7
3 : 7

num yield 8
filtered[0] 8 by 2

num yield 9
filter yield[0] 9
filtered[1] 9 by 3

num yield 10
filtered[0] 10 by 2

num yield 11
filter yield[0] 11
filter yield[1] 11
filter yield[2] 11
filter yield[3] 11
4 : 11

num yield 12
filtered[0] 12 by 2

num yield 13
filter yield[0] 13
filter yield[1] 13
filter yield[2] 13
filter yield[3] 13
filter yield[4] 13
5 : 13

num yield 14
filtered[0] 14 by 2

num yield 15
filter yield[0] 15
filtered[1] 15 by 3

num yield 16
filtered[0] 16 by 2

num yield 17
filter yield[0] 17
filter yield[1] 17
filter yield[2] 17
filter yield[3] 17
filter yield[4] 17
filter yield[5] 17
6 : 17

num yield 18
filtered[0] 18 by 2

num yield 19
filter yield[0] 19
filter yield[1] 19
filter yield[2] 19
filter yield[3] 19
filter yield[4] 19
filter yield[5] 19
filter yield[6] 19
7 : 19

num yield 20
filtered[0] 20 by 2

num yield 21
filter yield[0] 21
filtered[1] 21 by 3

num yield 22
filtered[0] 22 by 2

num yield 23
filter yield[0] 23
filter yield[1] 23
filter yield[2] 23
filter yield[3] 23
filter yield[4] 23
filter yield[5] 23
filter yield[6] 23
filter yield[7] 23
8 : 23

num yield 24
filtered[0] 24 by 2

num yield 25
filter yield[0] 25
filter yield[1] 25
filtered[2] 25 by 5

num yield 26
filtered[0] 26 by 2

num yield 27
filter yield[0] 27
filtered[1] 27 by 3

num yield 28
filtered[0] 28 by 2

num yield 29
filter yield[0] 29
filter yield[1] 29
filter yield[2] 29
filter yield[3] 29
filter yield[4] 29
filter yield[5] 29
filter yield[6] 29
filter yield[7] 29
filter yield[8] 29
9 : 29

参考:

通道 - Kotlin 官方文档 https://book.kotlincn.net/text/channels.html

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