Understand the effect of the constant factor hidden within the Big O. Often a O(n) algorithm is faster than a O(1) algorithm, because n is too small. E.g. array

Understand the effect of the constant factor hidden within the Big O. Often a O(n) algorithm is faster than a O(1) algorithm, because n is too small. E.g. arrays vs hashmaps. Make sure what n is in each case. For example a graph algorithm with O(n^2) and n being the number of nodes may actually be O(n) for n being the graph size (number of edges).