判断质数的两种方法

Posted 2020-08-03

<!--方法一, 删选法，通过排除有倍数关系的数-->
<script type="text/javascript">
    var arr = [];
    for(var i = 2; i < 200; i ++){
        for(var j  = 2 * i; j < 200; j += i){
            arr[j] = true;
        }
    }
    for(var i = 2; i < 200; i ++){
        if(arr[i] == undefined){
            document.write(i + "<br />");
        }
    }
</script>

<!--方法二-->
<script type="text/javascript">
    var arr = [];
    for(var i = 2; i < 200; i ++){
        arr[i] = true;
        for(var j =  2; j < i; j ++){
            if(i % j == 0){
                arr[i]  = false;
            }
        }
    }
    for(var i = 2; i < 200; i ++){
        if(arr[i] == true){
            document.write(i + "<br />");
        }
    }
</script>