## Research In Motion Interview Question for Software Engineer in Tests

Comment hidden because of low score. Click to expand.
1
of 1 vote

``````function isPrimeNumber(TestNumber) {
var SQRT_TestNumber=Math.floor(Math.sqrt(TestNumber));
var isPRIME=1;

for (var i=2;i<=SQRT_TestNumber;i++){
if ((TestNumber%i)==0) {
isPRIME=0;
break;
}
}

if(isPRIME==1){
printf(" Given number is prime ");
}
}``````

Comment hidden because of low score. Click to expand.
0

Every prime number is in the form of 6k+1 or 6k-1.
U can also use that property.

Comment hidden because of low score. Click to expand.
0

no that is wrong.. with the check of 6k, you're considering only divisibility by 2 and 3. what about those that are divisible by other primes. for eg: consider 25 = 6(4)+1, holds true for your check. but it is not prime.

Comment hidden because of low score. Click to expand.
0

1. Every composite number can be represented uniquely as multiple of Prime Numbers.
2. Since every prime number must in in the form of 6k+1 or 6k-1, just try to divide 4 <= x <= sqrt(num).
Where x is in the form of 6k+(-)1

Comment hidden because of low score. Click to expand.
0

@bvssatish
your solution will reduce the computation considerably.....nice method....
further optimization can be done by removing all even numbers between k and sqrt(num)...

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