javascript 如何在输入的数字范围内找到素数
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How to find prime numbers in entered number range
提问by user3027217
I'm just trying to find prime numbers of an entered range of numbers. I have no clue how to calculate finding primes. I need to add them to an array and output the array after. I put a placeholder for the calculation... I just can't seem to figure out how find the primes.
我只是想找到输入的数字范围的质数。我不知道如何计算求素数。我需要将它们添加到数组中并在之后输出数组。我为计算放置了一个占位符......我似乎无法弄清楚如何找到素数。
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>LeapYears</title>
<script type="text/javascript">
/* <![CDATA[ */
function calcPrimeNumber(){
var beginNum = document.numbers.firstNum.value;
var endNum = document.numbers.secondNum.value;
var primeNumbs = new Array();
var ctr = 0;
while (beginNum <= endNum){ //throwaway
if ((beginNum % beginNum == 0) && (beginNum % 1 == 0)){
primeNumbs[ctr] = beginNum;
++ctr;
}
++beginNum;
}
if (primeNumbs == 0){
window.alert("There were no leap years within the range.");
}
else {
outputPrimeNums(primeNumbs);
}
}
function outputPrimeNums(primes){
document.write("<h2>Prime Numbers</h2>");
for (i=0;i<primes.length;i++){
document.write(primes[i] + "<br/>");
}
}
/* ]]> */
</script>
</head>
<body>
<form name="numbers">
Beginning Number: <input type="text" name="firstNum" /> End Number: <input type="text" name="secondNum" />
<input type="button" value="Find Prime Numbers" onclick="calcPrimeNumber()" />
</form>
</body>
</html>
采纳答案by Satish Sharma
try this full page of prime no example
试试这整页的素数没有例子
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>LeapYears</title>
<script type="text/javascript">
/* <![CDATA[ */
function calcPrimeNumber(){
var beginNum = parseInt(document.numbers.firstNum.value);
var endNum = parseInt(document.numbers.secondNum.value);
var primeNumbs = new Array();
var ctr = beginNum;
while(ctr<=endNum)
{
if(isPrime(ctr)==true)
{
primeNumbs[primeNumbs.length] = ctr;
}
ctr = ctr+1;
}
if (primeNumbs.length == 0){
document.getElementById('output_content').innerHTML = "There were no prime no within the range.";
}
else {
outputPrimeNums(primeNumbs);
}
}
function isPrime(num)
{
var flag = true;
for(var i=2; i<=Math.ceil(num/2); i++)
{
if((num%i)==0)
{
flag = false;
break;
}
}
return flag;
}
function outputPrimeNums(primes){
var html = "<h2>Prime Numbers</h2>";
for (i=0;i<primes.length;i++){
html += primes[i] + "<br/>";
}
document.getElementById('output_content').innerHTML = html;
}
/* ]]> */
</script>
</head>
<body>
<form name="numbers">
Beginning Number: <input type="text" name="firstNum" /> End Number: <input type="text" name="secondNum" />
<input type="button" value="Find Prime Numbers" onclick="calcPrimeNumber()" />
</form>
<div id="output_content">
</div>
</body>
</html>
回答by john
You should use some algorithm to check whether a given no is prime no or not inside while loop . http://en.wikipedia.org/wiki/Prime_number
您应该使用一些算法来检查给定的 no 是否在 while 循环中是素数。 http://en.wikipedia.org/wiki/Prime_number
http://en.wikibooks.org/wiki/Efficient_Prime_Number_Generating_Algorithms
http://en.wikibooks.org/wiki/Efficient_Prime_Number_Generating_Algorithms
回答by Neil T
You need two loops here- the first to run between beginNumand endNumand the second to run from 1 to beginNumfor each value of beginNum in the outer loop.
这里需要两个循环——第一个在beginNum和之间endNum运行，第二个beginNum在外循环中从 1 到beginNum 的每个值运行。
Try replacing the main section of your code with the following. (For clarity, I'm going to introduce a new variable - numberBeingTested.)
尝试用以下内容替换代码的主要部分。（为清楚起见，我将引入一个新变量 - numberBeingTested。）
var ctr = 0;
var numberBeingTested = beginNum;
while (numberBeingTested <= endNum){ //throwaway
var testDivisor = 2;
var isPrime = true;
while (testDivisor < numberBeingTested ){ //throwaway
if (numberBeingTested % testDivisor == 0) {
isPrime = false;
}
++testDivisor;
}
if (isPrime){
primeNumbs[ctr] = numberBeingTested;
++ctr;
}
++numberBeingTested;
}
Note that there are many possible improvements here - for a start, this code as it stands will tell you that 1 is prime, and there are significant possible performance improvements (such as testing possible divisors up to the square root of the number being tested rather than the number itself) - but for your purposes it will probably suffice.
请注意，这里有许多可能的改进 - 首先，这段代码会告诉您 1 是质数，并且可能有显着的性能改进（例如测试可能的除数直到被测试数字的平方根，而不是比数字本身） - 但就您的目的而言，它可能就足够了。
回答by Pavel ?těrba
What I try was to edit Sieve of Atkin algorithmfrom linked question:
function getPrimes(min, max) {
var sieve = [], i, j, primes = [];
for (i = 2; i <= max; ++i) {
if (!sieve[i]) {
// i has not been marked -- it is prime
if (i >= min) {
primes.push(i);
}
for (j = i << 1; j <= max; j += i) {
sieve[j] = true;
}
}
}
return primes;
}
console.log(getPrimes(10, 100));
This will give you array with prime numbers from minto max. It still has to go through all number from 2, so maybe there will be more effective way how to achieve this.
这将为您提供从min到的素数数组max。它仍然必须从 2 开始遍历所有数字，所以也许会有更有效的方法来实现这一点。
