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Prime Checker

  • gidan24 + 1 comment

    Can you explain me why you check all odd numbers until square root of n? I don't understand why square root and not n/2..

    Anyway this is my working solution:

        private boolean isPrime(int n) {
        if (n < 2) {
            return false;
        }

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

        return true;
    }

    • RodneyShag + 0 comments

      because sqrt(n) * sqrt(n) = n.

      For example, if you want the factors of 100.

      1 * 100
2 * 50
4 * 25
5 * 20
10 * 10 <--- after this point the numbers (a,b) switch to become (b,a)
20 * 5
25 * 4
50 * 2
100 * 1

      HackerRank solutions.