1. Determine the time complexity of the following function and find its big-O notation.

int f1(int n)

{

int cnt = 0;

for (int p1 = 0; p1 <= n; p1++)

for (int p2 = 0; p2 <= n - p1; p2++)

cnt++;

return cnt;

}

I have found that the formula for time complexity is (n^2+n) / 2, however I cannot figure out how this was achieved. A step by step explanation if you don't mind, thank you.