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[js] 第50天 请写出一个函数求出N的阶乘（即N!） #191

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[js] 第50天 请写出一个函数求出N的阶乘（即N!）#191
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jsJavaScript
@haizhilin2013

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@haizhilin2013
haizhilin2013
opened on Jun 4, 2019
Collaborator

第50天 请写出一个函数求出N的阶乘（即N!）

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haizhilin2013
added
jsJavaScript
on Jun 4, 2019
cleverboy32

cleverboy32 commented on Jun 5, 2019

@cleverboy32
cleverboy32
on Jun 5, 2019
function factorial(n) {
      if (n > 1)  return n*factorial(n-1);
      return 1;
}
myprelude

myprelude commented on Jun 13, 2019

@myprelude
myprelude
on Jun 13, 2019
function getTotal(n){
  let s = 1,total;
  while(s<=n){
    total = 1*s;
    s++;
  }
  return total
}
Konata9

Konata9 commented on Jul 9, 2019

@Konata9
Konata9
on Jul 9, 2019
const stepNum = (num) => (num === 1 ? num : num * stepNum(num - 1));

console.log(stepNum(3))
console.log(stepNum(4))
console.log(stepNum(5))
console.log(stepNum(6))
wyx2014

wyx2014 commented on Jul 25, 2019

@wyx2014
wyx2014
on Jul 25, 2019
const getN = function (n,sum =1) {
   if(typeof n !=='number'){
       return '请输入数字类型'
   }
   if(n === 0){
       return sum;
   }else{
       sum = sum * n;
       return getN( --n ,sum);
   }
}
DingkeXue

DingkeXue commented on Aug 14, 2019

@DingkeXue
DingkeXue
on Aug 14, 2019
const getN = function (n,sum =1) {
   if(typeof n !=='number'){
       return '请输入数字类型'
   }
   if(n === 0){
       return sum;
   }else{
       sum = sum * n;
       return getN( --n ,sum);
   }
}

推荐这种写法，进行了尾递归优化，数值很大也不会出现内存溢出的问题

damofan

damofan commented on Sep 7, 2019

@damofan
damofan
on Sep 7, 2019 · edited by damofan
const getFactorial = n => {
	return new Array(n-1).join(',').split(',').reduce( total => { --n;  return total*n}, n)
}
JJL-SH

JJL-SH commented on Sep 24, 2019

@JJL-SH
JJL-SH
on Sep 24, 2019
function getN(num) {
  return Array.from(new Array(num)).reduce((cacheNum, it, index) => {
    return cacheNum * (index + 1);
  }, 1);
}
console.log(getN(6));
ZindexYG

ZindexYG commented on Oct 18, 2019

@ZindexYG
ZindexYG
on Oct 18, 2019
const factorial = num => {
  if (num > 1) 
    return num * factorial(num - 1)
  return 1
}

console.log(factorial(5))
huangd-d

huangd-d commented on Mar 30, 2020

@huangd-d
huangd-d
on Mar 30, 2020
function getTotal(n){
  let s = 1,total;
  while(s<=n){
    total = 1*s;
    s++;
  }
  return total
}

while( n>=1 ){
...
n--;
}
可以少个变量，感觉比递归方式，这样写舒服点。

xiaocaicaiaichicai

xiaocaicaiaichicai commented on Apr 15, 2020

@xiaocaicaiaichicai
xiaocaicaiaichicai
on Apr 15, 2020

这好像都没考虑位数限制

lizhesystem

lizhesystem commented on May 9, 2020

@lizhesystem
lizhesystem
on May 9, 2020 · edited by lizhesystem

判断了下如果小于0以及其他因素。

    function factorial(num) {
        let data = num;
        if (num < 0) return -1;
        if (num === 0 || num === 1) return 1;
        while (num > 1) {
            num--;
            data *= num;
        }
        return data;
    }

    console.log(factorial(5));  // 120
c37csq

c37csq commented on Jun 2, 2020

@c37csq
c37csq
on Jun 2, 2020

function getNum (num) {
let s = 1, total = 1;
while (s <= num) {
total = total * s
s ++
}
return total
}
console.log(getNum(5))

adi0754

adi0754 commented on Jun 16, 2020

@adi0754
adi0754
on Jun 16, 2020
function factorial(num, sum = 1) {
    if(num <= 1)return sum;
    sum *= num;
    return factorial(--num, sum);
}
waterkitten

waterkitten commented on Aug 9, 2020

@waterkitten
waterkitten
on Aug 9, 2020 · edited by waterkitten

正常递归会爆栈，所以要动态规划
var trailingZeroes = function(n) {
let arr=[1];
for(let i=1;i<n;i++){
arr[i]=arr[i-1]*(i+1)
}
return arr[n-1]

};

bozaigao

bozaigao commented on Oct 8, 2020

@bozaigao
bozaigao
on Oct 8, 2020
function tailDiGui(n, r) {
    if (n === 1) {
        return r;
    } else {
        return tailDiGui(n - 1, r * n)
    }
}

function jieCheng(n) {
    return tailDiGui(n, 1)
}
console.log(jieCheng(100));
bozaigao

bozaigao commented on Oct 17, 2020

@bozaigao
bozaigao
on Oct 17, 2020 · edited by bozaigao
function factorial(n) {
    if (isFinite(n) && n > 0 && Math.round(n)) {
        if (!(n in factorial)) {
            factorial[n] = n * factorial(n - 1)
        }

        return factorial[n]
    } else {
        return NaN;
    }
}

factorial[1] = 1;

console.log(factorial(1000));
smile-2008

smile-2008 commented on Nov 11, 2020

@smile-2008
smile-2008
on Nov 11, 2020
function factorial(n) {
      if (n > 1)  return n*factorial(n-1);
      return 1;
}
jamsehua

jamsehua commented on Jan 11, 2021

@jamsehua
jamsehua
on Jan 11, 2021
function getTotal(n){
  let s = 1,total;
  while(s<=n){
    total = 1*s;
    s++;
  }
  return total
}

上面这个不行，
function getTotal(n){
let s = 1,total=1;
while(s<=n){
total = total*s;
s++;
}
return total
}

xiaoqiangz

xiaoqiangz commented on Jun 6, 2022

@xiaoqiangz
xiaoqiangz
on Jun 6, 2022

function factorial(num, sum = 1) {
if (num < 1) {
return sum
}
sum *= num
return factorial(--num, sum)

panpanxuebing

panpanxuebing commented on Dec 12, 2024

@panpanxuebing
panpanxuebing
on Dec 12, 2024
function factorial (n) {
  if (n >  1) {
    return n * factorial(n - 1)
  }
  return 1
}

factorial(0) // 1
factorial(5) // 120
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          [js] 第50天 请写出一个函数求出N的阶乘（即N!） · Issue #191 · haizlin/fe-interview