1/*
2 * methods/gauss.c
3 *
4 * Calculate the sum of a given range of integer numbers.
5 *
6 * Somewhat of a more subtle way of calculation - and it even has a story
7 * behind it:
8 *
9 * Supposedly during math classes in elementary school, the teacher of
10 * young mathematician Gauss gave the class an assignment to calculate the
11 * sum of all natural numbers between 1 and 100, hoping that this task would
12 * keep the kids occupied for some time. The story goes that Gauss had the
13 * result ready after only a few minutes. What he had written on his black
14 * board was something like this:
15 *
16 * 1 + 100 = 101
17 * 2 + 99 = 101
18 * 3 + 98 = 101
19 * .
20 * .
21 * 100 + 1 = 101
22 *
23 * s = (1/2) * 100 * 101 = 5050
24 *
25 * A more general form of this formula would be
26 *
27 * s = (1/2) * (max + min) * (max - min + 1)
28 *
29 * which is used in the piece of code below to implement the requested
30 * function in constant time, i.e. without dependencies on the size of the
31 * input parameters.
32 *
33 */
34
35#**include** "gauss.h"
36
37
38**int** gauss_get_sum (**int** min, **int** max)
39{
40 /* This algorithm doesn't work well with invalid range specifications
41 so we're intercepting them here. */
42 **if** (max < min)
43 {
44 **return** 0;
45 }
46
47 **return** (**int**) ((max + min) * (**double**) (max - min + 1) / 2);
48}
49