How would you go about finding the complexity of this algorithm?

Question

function alg1(n)
1 a=0
2 for o=1 to n do
3     for t=1 to o do
4         for k=t to o+t do
5         a=a+1
6 return(a)

If anyone could guide me to how

Answer 1

We can compute the exact number of increments this code executes. First, let's replace

for k=t to o+t do

with

for k=1 to o+1 do 

After this change, two inner loops looks like this

for t=1 to o do
    for k=1 to o+1 do

The number of iterations of these loops is obviously o*(o+1). The overall number of iterations can be calculated in the following way:

We can exclude coefficients and lower order terms of the polynomial when using big-O notation. Therefore, the complexity is O(n^3).