Count Primes

Description:

Count the number of prime numbers less than a non-negative number, n.
题目的解题思路很经典https://leetcode.com/problems/count-primes/，见此链接的show Hint

JS代码如下：

var countPrimes = function(n) {    var count = 0,        arr=[]        map={};        map[true]=0;        map[false]=0;    if(n === 1 || n === 0)    {        return 0;    }    for(var k = 0; k < n; k++)    {        arr[k]=true;    }    arr[0]=false;    arr[1]=false;    // map.push(1);    // map.push(n);    for(var i = 2; i*i < n; i++)//只需检验i*i<n的数据    {         if((arr[i]===false))          {             continue;         }          for(var j = i*i; j < n; j+=i)//小于i*i以下的i的倍数已被赋值为false        {            arr[j]=false;        }    }     for(var x = 0; x < n; x++)    {        if(arr[x]) count++;    }    return count;};