A question about estimating the complexity of an algorithm?

Question

Algorithms

Guys why in the line where the i-th Fibonacci number is the time complexity is O (n)?
Thanks in advance.

Answer 1

Apparently, here it is considered how many times this line will be executed in total, and not how much it itself takes.
Because this line is in a loop that repeats O(n) times, then this line (which runs in constant time) will take O(n) in total.