How can I improve my counting prime numbers function?

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Java

public class Solution {
    public int countPrimes(int n) {
        if(n == 0){
            return 0;
        }
        int count = 0;
        for(int i = 2; i <= n; i++){
            if(!(n % i == 0)){
                count++;
            }
        }
        return count;
    }
}

What I have tried:

There are several cases that work for my code, but not all of them. For example, when n is assigned to 4, it doesn't count the two since 4 % 2 == 0. How can I fix this issue for not only this case but other cases as well?

Posted 6-Aug-16 7:21am

EpicKai

Updated 6-Aug-16 7:37am

v2

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Patrice T · Answer 1 · 2016-08-06T07:37:00

Quote:
How can I improve my counting prime numbers function?

there is nothing to improve, because what you have done is not working.
the whole logic of your code is to be reviewed.
Your logic actually say that i is a prime if not a divisor of n, it is plain wrong.
You need to create a function that tells you if a number is a prime and change your code to:

Java

public int countPrimes(int n) {
    if(n == 0){
        return 0;
    }
    int count = 0;
    for(int i = 2; i <= n; i++){
        if(IsPrime( i )){
            count++;
        }
    }
    return count;
}
public int IsPrime(int n) {
    // here you have to check if n is a prime
}