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  1. Practice
  2. Java
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  4. Prime Checker
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Prime Checker

  • tao_zhang + 3 comments

    Mine works

    import static java.lang.System.in;

class Prime {
    
    void checkPrime(int... args){
        String outPut = "";
        for (int arg : args){
            if (isPrime(arg)){
                outPut += arg+" "; 
            }
        }
        if (outPut != ""){
            outPut = outPut.substring(0,outPut.length()-1);
            System.out.print(outPut);
        }
        System.out.println();
    }
    
    boolean isPrime(int num){
        if (num < 2){
            return false;
        }
        for (int i = 2; i < (num/2)+1; i++){
            if (num%i==0){
                return false;
            }
        }
        return true;
    }
    
}
    • rafa_fr + 1 comment

      Very nice the import static.

      • [deleted] + 1 comment

        Can improve 

        for (int i = 2; i < (num/2)+1; i++){
            if (num%i==0){
                return false;
            }
        }

        as

        for (int i = 2; i*i <= num; i++){
            if (num%i==0){
                return false;
            }
        }

        will be faster

        • vlad_belon + 0 comments

          To avoid the i*i calculus in each loop:

          long maxDivider = Math.round(Math.sqrt(number));
for (int divider = 2; divider <= maxDivider; divider++) {
	if (number % divider == 0) {
		return false;
	}
}
    • RodneyShag + 1 comment

      Hi. For your isPrime() function, I see you iterated up to n/2. This gives you a runtime of O(n). Try iterating to square root of n like this for an O(n^(1/2)) runtime.

      Hope this helps.

      HackerRank solutions.

    • kalbatprog7 + 2 comments

      Sir how does the line checkprime(int... args), work? I am new to all this and I do not know what is int...? Please help!

      • rjvpillai364 + 1 comment

        It is basically called varargs or variable length arguments in java. The argument is specified with 3 periods(...) after the type. This syntax tells the compiler that the method can be called with 0 or more arguments. One thing to note here is that your method cannot have 2 varargs as arguments and varargs must always be last in method with more than 1 arguments. For example , void method(int... n1,int... n2) is invalid. void method(int... n1,int n2) is invalid, but void method(int n1,int... n2) is valid. It is logical since the compiler knows how many arguments to assign to varargs, thats why it should always be written last in the argument list

        • kalbatprog7 + 0 comments

          Thanks sir

      • qwertypsv + 0 comments
        [deleted]