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
