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Description:

Count the number of prime numbers less than a non-negative number, n.

java

public class Solution {
       public int countPrimes(int n) {        boolean[] a= new boolean[n];        for (int i=2;i*i

python

def countPrimes(n):    if n<=1:        return 0    elif n==2:        return 1    a={}    for i in range(2,n):        a.setdefault(i,None)    for i in range(2,n):        temp=n/i        for k in range(temp+1):            if k>1:                if k*i in a:                    a.pop(k*i)    return len(a)

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