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O(1) Constant – no loops. O(log N) Logarithmic – usually searching algorithms have log n if they are sorted (Binary Search). O(n) Linear – for loops, while loops through n items. O(n log(n)) Log Linear – usually sorting operations. O(n^2) Quadratic – every element in a collection needs to be compared to ever other element. Two nested loops. O(2^n) Exponential – recursive algorithms that solves a problem of size N. O(n!) Factorial – you are adding a loop for every element.