[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 · 2023-08-10T07:34:08Z

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);

pengshaowu · 2024-07-02T07:49:43Z

let arr = [];
function pushArr() {
   if (arr.length == 5) return console.log(arr);
   let num = Math.floor(Math.random() * (31 - 2) + 2);
   if (arr.indexOf(num) == -1) arr.push(num);
   pushArr();
}
pushArr();

13714273163 · 2024-07-02T07:50:21Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2024-07-02T07:50:38Z

您的来信已收到！谢谢 ——李方正

erpao7 · 2024-07-23T07:17:26Z

function foo(length, min, max) {
let result = [];
function bar() {
if (result.length === length) {
return;
}

      let randomNum = Math.floor(Math.random() * (max - min + 1));

      if (!result.includes(randomNum)) {
        result.push(randomNum);
      }
    }

    bar();
    return result;
  }
  const length = 5;
  const min = 2;
  const max = 32;
  const res = foo(length, min, max);

13714273163 · 2024-07-23T07:18:12Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2024-07-23T07:18:23Z

您的来信已收到！谢谢 ——李方正

pengsir120 · 2024-09-01T14:16:44Z

function fn(set = new Set()) {
if(set.size === 5) return Array.from(set)
set.add(Math.floor(Math.random() * 31) + 2)
return fn(set)
}

13714273163 · 2024-09-01T14:17:23Z

您好，邮件已收到，我会尽快回复。

lfz9527 · 2024-09-01T14:17:37Z

您的来信已收到！谢谢 ——李方正

msdlisper · 2024-09-06T02:44:32Z

const radomNum = () => {
  return Math.floor(Math.random() * 31 + 2)
}



const createArr = (arr) => {
  if (arr.length >= 5) {
    return arr;
  }
  const num = radomNum();
  if (arr.includes(num)){
    createArr(arr);
  } else {
    arr.push(num);
    createArr(arr)
  }
}


const res = createArr([])
console.log(res)

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

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haizhilin2013 commented Apr 17, 2019 • edited Loading

这一题是起源题

yxkhaha commented Apr 17, 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

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