This is my isPrime
method:
private static boolean isPrime(int num) {
if (num % 2 == 0) return false;
for (int i = 3; i * i < num; i += 2)
if (num % i == 0) return false;
return true;
}
I put isPrime(9)
and it returns true
. What is wrong with the method?
Your condition should be i * i <= num
private static boolean isPrime(int num)
{
if (num == 2)
return true;
if (num < 2 || num % 2 == 0)
return false;
for (int i = 3; i * i <= num; i += 2)
if (num % i == 0)
return false;
return true;
}
You didn't take number 9 in your consideration so 9<9 will result false. But you need to check 9.
my sample:
public boolean isPrime(int x) {
if (x==1) {
return true;
} else {
for(int i=2;i<=Math.sqrt(x);i++) {
if (x%i==0) return false;
}
}
return true;
}
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