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  1. Prepare
  2. Tutorials
  3. 30 Days of Code
  4. Day 19: Interfaces
  5. Discussions

Day 19: Interfaces

  • RodneyShag
     + 7 comments

    Efficient O(n^(1/2)) solution

    From my HackerRank solutions.

    Runtime: O(n^(1/2))
    Space Complexity: O(1)

    public int divisorSum(int n) {
    int sum = 0;
    int sqrt = (int) Math.sqrt(n);

    // Small optimization: if n is odd, we can't have even numbers as divisors
    int stepSize = (n % 2 == 1) ? 2 : 1;

    for (int i = 1; i <= sqrt; i += stepSize) {
        if (n % i == 0) { // if "i" is a divisor
            sum += i + n/i; // add both divisors
        }
    }

    // If sqrt is a divisor, we should only count it once
    if (sqrt * sqrt == n) {
        sum -= sqrt;
    }
    return sum;
}