Sum the odd-square numbers less than a given integer n.

issue-299-of-rendezvous-with-cassidoo.java

public class Main {
    public static void main(String[] args) {
        assert oddSquareSum(1) == 0;
        assert oddSquareSum(2) == 1;
        assert oddSquareSum(9) == 1;
        assert oddSquareSum(10) == 10;
        assert oddSquareSum(44) == 35;
        assert oddSquareSum(0) == 0;
        assert oddSquareSum(7569) == 105995;
        assert oddSquareSum(Integer.MAX_VALUE) == 16585052009610L;
    }

    // O(n) time & O(1) space - where n is the value of the integer input n
    public static long oddSquareSum(int n) {
        if (n < 0) {
            throw new IllegalArgumentException();
        }
        long sum = 0;
        long oddNum = 1;
        long oddSquareNum = 1;
        while (oddSquareNum < n) {
            sum += oddNum * oddNum;
            oddNum += 2;
            oddSquareNum = oddNum * oddNum;
        }

        return sum;
    }
}