I have encountered a few situations where time complexity matters during the normal course of work. The most notable one for me was where I did two DB queries t

I have encountered a few situations where time complexity matters during the normal course of work. The most notable one for me was where I did two DB queries to fetch a list of elements in one and another of the same length and related to the first one - to create a list of objects from the first list, I iterated on it, and it had to do another iteration inside to find the element in the second list. It turned out this approach showed some performance problems on larger datasets, so another coworker took a look at optimizing it - he ended up grouping the second list by id in one iteration so that it eliminated the need to iterate again inside the loop, transforming it from time complexity O(n^2) to O(n). These situations don't come up too often, but when they do, it becomes important to at least be able to solve them in some fashion in a non-high pressure situation.