| /* |
| * methods/gauss.c |
| * |
| * Calculate the sum of a given range of integer numbers. |
| * |
| * Somewhat of a more subtle way of calculation - and it even has a story |
| * behind it: |
| * |
| * Supposedly during math classes in elementary school, the teacher of |
| * young mathematician Gauss gave the class an assignment to calculate the |
| * sum of all natural numbers between 1 and 100, hoping that this task would |
| * keep the kids occupied for some time. The story goes that Gauss had the |
| * result ready after only a few minutes. What he had written on his black |
| * board was something like this: |
| * |
| * 1 + 100 = 101 |
| * 2 + 99 = 101 |
| * 3 + 98 = 101 |
| * . |
| * . |
| * 100 + 1 = 101 |
| * |
| * s = (1/2) * 100 * 101 = 5050 |
| * |
| * A more general form of this formula would be |
| * |
| * s = (1/2) * (max + min) * (max - min + 1) |
| * |
| * which is used in the piece of code below to implement the requested |
| * function in constant time, i.e. without dependencies on the size of the |
| * input parameters. |
| * |
| */ |
| |
| #include "gauss.h" |
| |
| |
| int gauss_get_sum (int min, int max) |
| { |
| /* This algorithm doesn't work well with invalid range specifications |
| so we're intercepting them here. */ |
| if (max < min) |
| { |
| return 0; |
| } |
| |
| return (int) ((max + min) * (double) (max - min + 1) / 2); |
| } |
