Why we Need It one problem has many solutions but which solution is best is decided by big O in mathematical terminology Who cares In a real-life scenario it's just your program should work you should provide an outcome to it .how it works really doesn't matter but it matters in interviews or if you have big(VERY BIG) data structure Units To decide which one is better More reliable units are faster and less memory though readability is very relevant but we don't measure it on the basis of it. On The basis of time See in snippet(code) why you should not use time If same algo is run is super computer than it will run fast and if same algo run in old version computer it will run slow so moral of the story is you cannot depend on time If not Time Than what Better way is to count the number of operation computer has to perform.I have two examples first we will look at second example how many operation it is doing (*,+,/)=>so 3 operation which will always remain same whatever...