閑來看了一篇部落格：閑聊質數，看後自己動手研究了輸出質數的方法，計算質數的效率有所提高.
下面是改進後的代碼：
使用索引儲存質數<!DOCTYPE HTML><html><head> <meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0" name="viewport" /> <title>prime</title> <style> #wrap{ width:320px; margin:0 auto; text-align: center; } #output{ text-align:left; } var{ color:red; } </style></head><body><div id="wrap"> <h1>算質數</h1> <br> <div> <input id="max" type="text" />以內的質數 <input type="button" id="button" value="計算" /> </div> <br> <div id="output"></div></div><script>button.onclick = function() { var value = max.value; output.innerHTML = "<var>計算中...</var>"; if (value) { //擷取質數數組 var startTime = (new Date()).getTime(); var arr = getPrime2(parseInt(value)); var nowTime = (new Date()).getTime(); var time = (nowTime - startTime) / 1000; // var str = arrToString(arr); str = "<strong>" + value + "</strong> 以內的質數有<strong> " + arr.length + " </strong>個：<var>（計算耗時" + time + "秒）</var><br>" + str; // output.innerHTML = str; } else { output.innerHTML = "<var>請輸入素數的範圍</var>"; }}function arrToString(arr) { //數組轉化為字串 return arr.join(" ");}function getPrime2(max) { //擷取max以內的質數 var prime = []; for (var i = 2; i <= max; i++) { if (isPrimeNum(i, prime)) { prime.push(i); } } return prime;}function isPrimeNum(n, arr) { if (n < 2) { return false; } if (n == 2) { return true; } if (!arr || !arr.length) { return false; } for (var p = 0; p < arr.length; p++) { if (n % arr[p] == 0) { return false; } } return true;}</script></body></html>
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