Big O notation cheatsheet

O(1)       - array index
O(n)       - foreach array
O(log n)   - binary search
O(n log n) - merge sort
O(n²)      - foreach inside foreach (squared)
O(n³)      - foreach inside foreach inside foreach (cubic)
O(2^n)     - fibanachi
O(n!)      - go throuth graph

Simplifying:

O(2n)        => O(3n) => O(n)
O(n + n²)    => O(n²)
O(n²/2)      => O(n²)
O(n + log n) => O(n)
O(60 * 2^n + 10*n^100) => O(2^n + n^100) => O(2^n)
O(n² + m)             => O(n² + m)