Subject | Algorithm Design |
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NU Year | Set: 1.(c) Marks: 5 Year: 2009 |

Having a close look at the program we notice that it consists of two nested for-loops. In both loops the variables run from 0 to n, but the inner variable starts right from where the outer one just stands. An `if` with a comparison and some assignments not necessarily executed reside inside the two loops. A good measure for the running time is the number of executed comparisons. In the first iteration n comparisons take place, in the second n-1, then n-2, then n-3 etc. So 1+2+...+n comparisons are performed altogether. According to the well known Gaussian sum formula these are exactly 1/2·(n-1)·n comparisons. The screened area corresponds to the number of comparisons executed. It apparently corresponds approx. to half of the area of a square with a side length of n. So it amounts to approx. 1/2·n^{2}.