[js] 第1天用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 #3

haizhilin2013 · 2019-04-17T04:59:40Z

这一题是起源题

描述：

这是一道大题目，把考点拆成了4个小项；需要侯选人用递归算法实现（限制15行代码以内实现；限制时间10分钟内完成）：
a) 生成一个长度为5的空数组arr。
b) 生成一个（2－32）之间的随机整数rand。
c) 把随机数rand插入到数组arr内，如果数组arr内已存在与rand相同的数字，则重新生成随机数rand并插入到arr内[需要使用递归实现，不能使用for/while等循环]
d) 最终输出一个长度为5，且内容不重复的数组arr。

yxkhaha · 2019-04-17T11:07:20Z

    var arr = new Array(5);
    var num = randomNumber();
    var i = 0;
    randomArr(arr,num);
    function randomArr(arr,num) {
        if (arr.indexOf(num)< 0){
            arr[i] = num;
            i++;
        } else {
            num = randomNumber();
        }
        if (i>=arr.length){
            console.log(arr);
            return;
        }else{
            randomArr(arr,num)
        }
    }
    function randomNumber() {
        return Math.floor(Math.random()*31 + 2)
    }

qingleizhang123 · 2019-04-17T15:08:40Z

haizhilin2013 · 2019-04-18T00:03:15Z

点评：
知识点：递归、随机数
难点：1颗星
这道题主要是想考递归的用法，同时顺带考了生成指定范围的随机数方法。
@yxkhaha @qingleizhang123

qq674785876 · 2019-05-05T07:09:17Z

hellojackhui · 2019-05-06T10:47:08Z

var arr = new Array(5);
var num = Math.floor(Math.random()* (31) + 2);
function numsInterative(num) {
  if (arr.length == 5) {
    console.log(arr);
  }
  if (!arr.includes(num)) {
    arr.push(num)
  }
  numsInterative(Math.floor(Math.random()* (31) + 2))
}
numsInterative(num)

shulandmimi · 2019-05-07T07:53:46Z

    var arr = new Array(5),
          len = arr.length;
    function arPush() {
        if( len != 0 ) {
            len --;
            let n = Math.floor((Math.random() * 31) + 2);
            each(n, len) ? (arr[len] = n) : len ++;
            arPush();
        }
    }
    function each(index, i) {
        if( i > arr.length - 1) return true; 
        return arr[i] == index ? false : (each(index,i + 1));
    }
    arPush()

IronManSuper · 2019-05-07T08:46:37Z

var arr = new Array(5);
var i= 0;
function randomHandle () {
var num = 2 + Math.floor(Math.random() * 30);
if (arr.indexOf(num) < 0) {
arr[i] = num;
i ++;
}
(i < 5) && randomHandle();
}
randomHandle();

linghucq1 · 2019-05-08T03:51:06Z

考虑一下扩展性

function insertArr(arr, i = 0, min = 2, max = 32) {
  const num = Math.max(min, Math.ceil(Math.random() * max))
  if (!arr[arr.length - 1]) {
    if (!arr.includes(num)) { 
      arr[i++] = num
    }
    return insertArr(arr, i) 
  }
  return arr 
}
const arr = new Array(5);
const result = insertArr(arr)

这里的随机数算法是有问题的，具体参见下面 @likeke1997 的答案。另外用四舍五入也是不对的，因为最小值和最大值只有其它值概率的一半。

仔细一看，虽然自定义了最大最小参数，但是递归的时候没有传入，所以并没有卵用。i 参数的初衷是自定义从哪里开始插入，实用性也没有 @likeke1997 的 length 参数来的好。

Magty · 2019-05-08T07:04:03Z

function getUNumber(arr, min, max) {
var rand = Math.floor(Math.random() * (max - 1)) + min;
if (arr.indexOf(rand) === -1) {
return rand;
} else {
return getUNumber(arr, min, max);
}
}

function getRandomArrayByLength(len) {
    if (len === 1) {
        return [getUNumber([], 2, 32)];
    } else {
        var arr = getRandomArrayByLength(len - 1);
        var rand = getUNumber(arr, 2, 32);
        arr.push(rand);
        return arr;
    }
}

var newArray = new Array(5);
console.log(getRandomArrayByLength(newArray.length));

iCharlesZ · 2019-05-08T10:20:56Z

var arr = new Array(5);
function insertRandom(n) {
  if (n < 0) return
  let tmp = Math.floor(Math.random() * 31 + 2)
  if (arr.indexOf(tmp) !== -1) return insertRandom(n)
  arr[n] = tmp
  return insertRandom(n - 1)
}
insertRandom(arr.length - 1)

lqwzjay · 2019-05-10T01:50:00Z

  function getRandomArr(arr, len,) {
    if (arr.length === len) { return arr }
    let rndNum = Math.floor(Math.random() * (32 - 2 + 1) + 2)
    if (arr.indexOf(rndNum) > -1) return getRandomArr(arr, len)
    else {
      arr.push(rndNum)
      return getRandomArr(arr, len)
    }
  }
  console.log(getRandomArr([], 5))

Lucas-Lulululu · 2019-05-10T01:52:28Z

function createArr(arr) {
let res = arr || [];
let num = parseInt(Math.random() * (32 - 2) + 2);
if (!res.includes(num)) res.push(num);
if (res.length < 5) createArr(res)
return res
}
let b = createArr()

hcxowe · 2019-05-10T07:03:53Z

function foo(arr) {
	arr = arr || []

	if (arr.length >= 5) {
		return arr
	}

	var n = 2 + Math.floor(Math.random() * 31)

	if (arr.indexOf(n) == -1) {
		arr.push(n)
	}

	return foo(arr)
}

qianchenY · 2019-05-11T08:25:47Z

function randomNum(){
    return Math.floor(Math.random() * 32 + 2)
}
function arrFunc(arr, num){
    if(arr.length >= 5) return arr;
    if(!arr.includes(num)){
	arr.push(num);
    }
    return arrFunc(arr, randomNum())
}
arrFunc(arr, randomNum())

ouyinheng · 2019-05-14T02:01:13Z

function setArr(arr) {
      if(arr.length==5) return;
      const num = parseInt((Math.random())*31+2);
      if(arr.indexOf(num) === -1) arr.push(num)
      return setArr(arr);
}

tzjoke · 2019-05-16T11:05:32Z

function buildArray(arr, length, min, max) {
    if (!Array.isArray(arr)) arr = []
    if (length < 1) return []
    if (arr.length === length) return arr
    const random = Math.random() * (+max - +min) + +min
    if (!arr.includes(random)) arr.push(random)
    return buildArray(arr, length, min, max)
}

buildArray([], 5, 2, 32)

hbxywdk · 2019-05-17T08:36:52Z

function createArray(len, minNum, maxNum) {
  var createRandom = (min, max) => { return (Math.round((max - min) * Math.random()) + min)};
  var arr = new Array(len), count = 0;
  function run() {
    var num = createRandom(minNum, maxNum);
    (!arr.includes(num)) && (arr[count] = num, count++);
    (count < len) && (run());
  }
  run(); return arr;
}
console.log(createArray(5, 2, 32));

readream · 2019-05-19T11:06:42Z

var arr = []
var num 
console.log(num)
function newArr(arr, num) {
  if (arr.length >= 5) {
    return
  } else {
    num = Math.floor(Math.random() * 30) + 2
    return arr.push(num) + newArr(arr, num)
  }
}
newArr(arr, num)
console.log(arr)

ghost · 2019-05-23T05:01:38Z

function returnRandomArr(max, min, length, arr = []) {
  arr.push(Math.floor(Math.random() * (max - min)) + min);
  arr = Array.from(new Set(arr))
  return arr.length < length ? returnRandomArr(max, min, length, arr) : arr
}
let arr = returnRandomArr(32, 2, 5)
console.log(arr)

yangchunboy · 2019-05-27T02:03:40Z

const arr = []
const getRandom = () => {
	const num = parseInt(Math.random() * 100, 10) + 2
	if (arr.length >= 5) return arr
	if (num <= 32 && arr.indexOf(num) === -1){
		arr.push(num)
		getRandom()
	} else {
		getRandom()
	}
}
getRandom()
console.log(arr)

yangchunboy · 2019-05-27T02:06:08Z

const arr = []
const getRandom = () => {
	const num = parseInt(Math.random() * 100, 10) + 2
	if (arr.length >= 5) return arr
	if (num <= 32 && arr.indexOf(num) === -1){
		arr.push(num)
	}
	getRandom()
}
getRandom()
console.log(arr)

sunbigshan · 2019-05-28T07:27:46Z

// 尾递归
function randomArr(count, arr = []) {
  if(count === 0) return arr;
  let num = Math.floor(Math.random() * 31) + 2;
  if(!arr.includes(num)) {
    arr.push(num);
    count--;
  }
  return randomArr(count, arr);
}

console.log(randomArr(5))

likeke1997 · 2019-06-05T07:33:00Z

// 6 行写完
function buildArray(arr, length, min, max) {
    var num = Math.floor(Math.random() * (max - min + 1)) + min;
    if (!arr.includes(num)) { arr.push(num); }
    return arr.length === length ? arr : buildArray(arr, length, min, max);
}
var result = buildArray([], 5, 2, 32);
console.table(result);

补充：
题目要求”生成一个（2－32）之间的随机整数rand“，既然是随机，我觉得意为取值到区间内各数的概率应该是相等的。所以像这样的写法是不严谨的：

// 在 2 - 5 区间内生成随机数
var min = 2, max = 5;
var result = Math.max(min, Math.ceil(Math.random() * max));
// 参数一 param1 恒等于 2
// 参数二 param2 在 [0, 5] 之间等概取值
// 可能性见下
// param1 2 2 2 2 2 2
// param2 0 1 2 3 4 5
// result 2 2 2 3 4 5

可见 result 取到 2 的概率大于 3/4/5。 @linghucq1

abin-jb · 2019-06-12T23:16:42Z

为啥要 return insertArr(arr, i) ,把return去掉也可以

leisurele · 2019-06-16T08:19:38Z

    let randomArr = [];
    function recursiveNumber(randomArr, currentLoop,min, max) {
        if (currentLoop <= 0) return;
        const curRandomNumber = min + parseInt(Math.round(Math.random() * (max -min)));
        if (randomArr.filter(res => res === curRandomNumber).length) {
            recursiveNumber(randomArr, currentLoop, min, max);
        } else {
            randomArr.push(curRandomNumber);
            recursiveNumber(randomArr, currentLoop - 1, min, max);
        }
    };
    recursiveNumber(randomArr, 5, 2, 32);

这是我的答案，大家可以参考下

Damon99999 · 2019-06-17T13:02:31Z

function outPut() {
	var num = Math.random()*10+2;
	if(set.size <= 5) {
		set.add(Math.round(num));
		outPut();
	} else {
	        console.log([...set]);
	}
}
var set = new Set();
outPut();

AricZhu · 2019-06-18T00:38:35Z

FEJiuL · 2019-06-20T08:28:19Z

`
function main(len = 5){

let list = [];

for(let i = 2; i <= 32; i++){   // 这里生成取值范围列表

	list.push(i);

}

function getRandom(start, end){

	let rang = end - start;

	return Math.floor(Math.random() * rang) + start;

}

function recursion(arr = []){

	let index = getRandom(0, list.length);

	let val = list.splice(index, 1).join();  //随机到后移除出列表(可避免随机到重复值)

	arr.push(val);

	return arr.length >= len ? arr : recursion(arr);  //根据结束条件去递归

}

return recursion();

}
`

persist-xyz · 2019-06-26T08:34:18Z

function buildArray2 () {
        // Set实现
        function createRandom () {
            return Math.floor(Math.random() * 30 + 2)
        }
        let arr = new Set()
        function arrayRandom () {
            if (arr.size < 5) {
                arr.add(createRandom())
                arrayRandom()
            } else {
                arr = [...arr]
                console.log('---' + arr)
            }
        }
        arrayRandom()
    }

lfz9527 · 2023-04-26T17:22:33Z

您的来信已收到！谢谢 ——李方正

R-magician · 2023-05-15T05:42:25Z

let setNumber=(arry:any)=>{
let nu:any = Number(Math.random()*31+2).toFixed(0)
let fn:any = ()=>{
if(arry.includes(nu)){
nu = Number(Math.random()*31+2).toFixed(0)
return fn(arry)
}else{
arry.push(nu)
return setNumber(arry)
}
}
if(arry.length<5){
return fn()
}else{
return arry
}
}
setNumber([])

13714273163 · 2023-05-15T05:42:52Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2023-05-15T05:43:03Z

您的来信已收到！谢谢 ——李方正

Athony1225 · 2023-05-20T07:41:00Z

Frontendnightmare · 2023-05-24T01:13:31Z

const arr = new Array(5);
const rand = Math.random() * 31 + 2;//包括2和32
const randInsertarr = (n) => {
    if (n == -1) {
        return arr;
    }
    const rand = Math.trunc(Math.random() * 31 + 2)//trunc取整
    if (!arr.includes(rand)) arr[n] = rand
    return randInsertarr(n - 1)
}
console.log(randInsertarr(arr.length - 1));

cpploved · 2023-06-27T08:44:53Z

let arr = []
function rand(min = 2, max = 32) {
return Math.max(min, Math.ceil(Math.random() * max))
}
function setArr(arr, num) {
if (arr.includes(num)) {
setArr(arr, rand())
} else {
arr.push(num)
}
}
while (arr.length < 5) {
setArr(arr, rand())
}

lfz9527 · 2023-06-27T08:45:33Z

您的来信已收到！谢谢 ——李方正

wmasfoe · 2023-08-10T07:33:25Z

const arr = new Array(5)
function pushNum(array = [], index = 0) {
    const rand = Math.floor(Math.random() * 31 + 2)
    if(index === 5) {
        return array
    }
    if(arr.includes(rand)) {
        pushNum(array, index)
    } else {
        array[index] = rand
        pushNum(array, index + 1)
    }
}
pushNum(arr)
console.log(arr)

13714273163 · 2023-08-10T07:33:51Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2023-08-10T07:34:08Z

您的来信已收到！谢谢 ——李方正

gavawu · 2023-09-07T08:55:42Z

const arr = []
const pushItem = function(arr){
  if(arr.length<5){
     const randomNum = Math.floor(Math.random()*31 + 2)
     if(!arr.includes(randomNum)){
        arr.push(randomNum)
        pushItem(arr)
        return
     }else{
        pushItem(arr)
     }
  }
 
}

13714273163 · 2023-09-07T08:56:15Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2023-09-07T08:56:30Z

您的来信已收到！谢谢 ——李方正

0726m · 2023-09-22T02:56:31Z

// 生成指定范围的随机数
function getRandomNumber(min,max){
    return Math.floor(Math.random() * (max - min + 1)) +min;
}
// 检查数组中是否有重复的数
function hasDuplicates(array,num){
    return array.includes(num);
}
// 生成指定长度且元素不重复的随机数数组
function generateUniqueRandomArray(array,length){
    if(array.length === length){
        return array;
    }
    const randomNum = getRandomNumber(2,32);
// 如果生成的随机数在数组中已存在，则重新生成
    if(hasDuplicates(array.randomNum)){
        return generateUniqueRandomArray(array,length);
    }
    array.push(randomNum);
    return generateUniqueRandomArray(array,length);
}
const resultArray = generateUniqueRandomArray([],5);
console.log(resultArray);

lfz9527 · 2023-09-22T02:57:18Z

您的来信已收到！谢谢 ——李方正

Maureen-Lee · 2023-09-22T03:56:44Z

你好邮件已收到

lfz9527 · 2023-11-07T03:43:49Z

您的来信已收到！谢谢 ——李方正

zzyouyou · 2023-11-07T03:45:52Z

const insert=(arr)=>{
const val = Math.floor(Math.random()*31)+2;
    if(!arr.includes(val)){
        arr.push(val);
    }
    if(arr.length<6) insert(arr);
}

let val=[];
insert(val);

caiwuu · 2024-01-09T04:29:07Z

function genArr(res=[]) {
  const value =  Math.floor(Math.random()*31 + 2)
  if(res.indexOf(value)<0) return (res.push(value)<5 && genArr(res),res)
  return genArr(res) 
}

13714273163 · 2024-01-09T04:29:09Z

您好，邮件已收到，我会尽快回复。

lxt-ing · 2024-01-09T04:29:15Z

你的邮件我已收到，我会尽快处理

lfz9527 · 2024-01-09T04:29:29Z

您的来信已收到！谢谢 ——李方正

angrybird233 · 2024-02-26T08:15:28Z

const result = getUniqueRandomNumbers([],5);
console.log(result)

lfz9527 · 2024-02-26T08:16:19Z

您的来信已收到！谢谢 ——李方正

usercci · 2024-03-05T08:43:46Z

const createRandomNum = () => { return Math.floor(Math.random(0, 1) * 31) + 2; }; const createRandomArray = (array, num, i) => { if (!array.includes(num)) { array[i] = num; i++; } else { num = createRandomNum(); } if (i >= array.length) { console.log(array); return; } else { createRandomArray(array, num, i); } }; createRandomArray(new Array(5), createRandomNum(), 0);

usercci · 2024-03-05T08:46:07Z

const createRandomNum = () => {
      return Math.floor(Math.random(0, 1) * 31) + 2;
    };
    const createRandomArray = (array, num, i) => {
      if (!array.includes(num)) {
        array[i] = num;
        i++;
      } else {
        num = createRandomNum();
      }
      if (i >= array.length) {
        console.log(array);
        return;
      } else {
        createRandomArray(array, num, i);
      }
    };
    createRandomArray(new Array(5), createRandomNum(), 0);

haizhilin2013 added the js JavaScript label Apr 18, 2019

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[js] 第1天 用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 #3

[js] 第1天 用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 #3

Comments

haizhilin2013 commented Apr 17, 2019 • edited

这一题是起源题

yxkhaha commented Apr 17, 2019

qingleizhang123 commented Apr 17, 2019

haizhilin2013 commented Apr 18, 2019

qq674785876 commented May 5, 2019

hellojackhui commented May 6, 2019

shulandmimi commented May 7, 2019

IronManSuper commented May 7, 2019

linghucq1 commented May 8, 2019 • edited

Magty commented May 8, 2019

iCharlesZ commented May 8, 2019 • edited

lqwzjay commented May 10, 2019

Lucas-Lulululu commented May 10, 2019

hcxowe commented May 10, 2019

qianchenY commented May 11, 2019 • edited

ouyinheng commented May 14, 2019 • edited

tzjoke commented May 16, 2019

hbxywdk commented May 17, 2019

readream commented May 19, 2019 • edited

ghost commented May 23, 2019

yangchunboy commented May 27, 2019

yangchunboy commented May 27, 2019

sunbigshan commented May 28, 2019 • edited

likeke1997 commented Jun 5, 2019 • edited

abin-jb commented Jun 12, 2019

leisurele commented Jun 16, 2019

Damon99999 commented Jun 17, 2019 • edited

AricZhu commented Jun 18, 2019

FEJiuL commented Jun 20, 2019 • edited

persist-xyz commented Jun 26, 2019 • edited

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usercci commented Mar 5, 2024

[js] 第1天用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 #3

[js] 第1天用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 #3

haizhilin2013 commented Apr 17, 2019 •

edited

linghucq1 commented May 8, 2019 •

edited

iCharlesZ commented May 8, 2019 •

edited

qianchenY commented May 11, 2019 •

edited

ouyinheng commented May 14, 2019 •

edited

readream commented May 19, 2019 •

edited

sunbigshan commented May 28, 2019 •

edited

likeke1997 commented Jun 5, 2019 •

edited

Damon99999 commented Jun 17, 2019 •

edited

FEJiuL commented Jun 20, 2019 •

edited

persist-xyz commented Jun 26, 2019 •

edited

wmasfoe commented Aug 10, 2023 •

edited

gavawu commented Sep 7, 2023 •

edited