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JavaScript使用高階生成器進行過濾以生成素數(shù)

更新時間：2024年02月23日 16:05:38 作者：42

生成器大家都知道是怎么一回事,但是高階生成器又是什么東西呢,下面小編就來為大家簡單介紹一下如何使用高階生成器進行過濾以生成素數(shù)吧

生成器大家都知道是怎么一回事，但是高階生成器又是什么東西呢？今天小編就帶著大家來一起了解一下吧……

先上代碼：

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)
    }
}

結(jié)果：

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

其中函數(shù) filter 傳入一個生成器，返回一個新的生成器，我們可以把它稱為高階生成器。

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

它的作用是過濾掉 nums: Generator<number> 生成的數(shù)中能被 prime 整除的數(shù)：

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

結(jié)果：

10
11
13
14
16
17
19
20
22
23

可以看到，3 的倍數(shù)，12、15、18、21 已經(jīng)被過濾掉了。

如果我們再把函數(shù)返回值作為參數(shù)傳給 filter，就能過濾掉多個值了：

let gen = filter(numFrom(10), 3) // 從 10 開始，不能被 3 整除的數(shù)
gen = filter(gen, 5) // 從 10 開始，不能被 3 和 5 整除的數(shù)
...

只要我們不斷把當前的生成器和產(chǎn)生的素數(shù)傳入，我們就能夠?qū)崿F(xiàn)過濾，相當于使用篩法生成素數(shù)。

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) // 產(chǎn)生新的生成器
    }
}

numFrom(2) -> filter(2) -> filter(3) -> filter(5) -> filter(7) ...

如果還不太清除，可以在控制臺打印詳細過程：

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)
    }
}

結(jié)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