IistPrimes 문제 풀이

문제

 

내가 짠코드

public class Solution { 
	public String listPrimes(int num) {
    // TODO:
		int[] arr = new int[num-1];
		int j = 0;
		String result = "";
		if(num<=2) return result+=num;
		else result = "2";
		
		for(int i=3;i<=num;i++){
			for(j=2;j<=i;j++){
					if(i%j==0) break;
				}
				if(i==j) result= result + "-" + i;
				
		}
		return result;
	} 
}

 

 

reference

public class Solution { 
	public String listPrimes(int num) {
    String result = "2";
		for (int candi = 3; candi <= num; candi += 2) {
			boolean isPrime = true;
			int sqrt = (int) Math.sqrt(candi);
			for (int divider = 3; divider <= sqrt; divider += 2) {
				if (candi % divider == 0) {
					isPrime = false;
					break;
				}
			}

			if (isPrime) {
				result = result + "-" + candi;
			}
		}

		return result;
	} 
}