# How do you calculate the big O of an algorithm

I have a problem where i have to find missing numbers within an array and add them to a set.

The question goes like so:

Array of size (n-m) with numbers from 1..n with m of them missing.

Find one all of the missing numbers in O(log). Array is sorted. Example:

n = 8

arr = [1,2,4,5,6,8]

m=2

Result has to be a set {3, 7}.

This is my solution so far and wanted to know how i can calculate the big o of a solution. Also most solution I have seen uses the divide and conquer approach. How do i calculate the big oh of my algorithm below ?

ps If i don't meet the requirement, Is there any way I can do this without having to do it recursively ? I am really not a fan of recursion, I simply cant get my head around it ! :(

``````var arr = [1,2,4,5,6,8];
var mySet = [];

findMissingNumbers(arr);

function findMissingNumbers(arr){
var temp = 0;
for (number in arr){                    //O(n)
temp = parseInt(number)+1;
if(arr[temp] - arr[number] > 1){
}
}
}