Question

For the following program segments, write a program that shows the estimated runtime for each piece. Run it on your computer when n=1, 10, 100, 1000, 10000, 100000, 1000000 for ten times each so that you can observe the differences in performance among these segments.

Segment1:        for (sum=0, i=1; i<=n; i++)

                        sum = sum + i;

Segment2:        for (sum=0, i=1; i<=n; i++)

                                                for (j=1; j<=i; j++)

                                                            sum++;

Segment3:        sum= n * (n+1)/2

Answer 1

public class ShowTimes {

        public static long sum1(int n) {
                long start = System.nanoTime();
                int sum, i;
                for (sum = 0, i = 1; i <= n; i++)
                        sum = sum + i;
                long end = System.nanoTime();

                return (end - start);
        }

        public static long sum2(int n) {
                long start = System.nanoTime();
                int sum, i, j;
                for (sum = 0, i = 1; i <= n; i++)
                        for (j = 1; j <= i; j++)
                                sum++;
                long end = System.nanoTime();

                return (end - start);
        }

        public static long sum3(int n) {
                long start = System.nanoTime();
                int sum = n * (n + 1) / 2;
                long end = System.nanoTime();

                return (end - start);
        }

        public static void main(String[] args) {

                int sizes[] = new int[] { 1, 10, 100, 1000, 10000, 100000, 1000000 };

                System.out.printf("%-15s%-10s%-10s%-10s\n", "InputSize", "Segment1", "Segment2", "Segment3");

                for (int size : sizes) {
                        System.out.printf("%-15d%-10d%-10d%-10d\n", size, sum1(size), sum2(size), sum3(size));

                }

        }

}

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