 <p>A very popular O(n log n) algorithm is merge sort. <a href="http://en.wikipedia.org/wiki/Merge_sort" rel="nofollow">http://en.wikipedia.org/wiki/Merge_sort</a> for example of the algorithm and pseudocode. The log n part of the algorithm is achieved through breaking down the problem into smaller subproblems, in which the height of the recursion tree is log n.</p> <p>A lot of sorting algortihms has the running time of O(n log n). Refer to <a href="http://en.wikipedia.org/wiki/Sorting_algorithm" rel="nofollow">http://en.wikipedia.org/wiki/Sorting_algorithm</a> for more examples.</p>