A month ago, I went on a performance quest trying to optimize a PHP script that took 5 days to run. Together with the help of many talented developers, I eventually got it to run in under 30 seconds.

When people say leetcode interviews are pointless I might share a link to this post. If that sort of optimization is possible there is a structures and algorithms problem in the background somewhere.

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nicoburns 8 hours ago | parent | next [-]

I find that these kind of optimizations are usually more about technical architecture than leetcode. Last time I got speedups this crazy the biggest win was reducing the number of network/database calls. There were also optimisations around reducing allocations and pulling expensive work out of hot loops. But leetcode interview questions don't tend to cover any of that.

They tend to be about the implementation details of specific algorithms and data structures. Whereas the important skill in most real-world scenarios would be to understand the trade-offs between different algorithms and data structures so that you pick an appropriate off-the-shelf implementation to use.

	▲	LollipopYakuza 7 hours ago \| parent [-]
		I agree. The "advanced" leetcode is about those last % of optimization. But when network latency is involved in a flow, it is usually the most obvious low hanging fruit.

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tuetuopay 7 hours ago | parent | prev | next [-]

Well leetcode asks you to implement the data structure, not how and when to use which data structure. I don’t need to know how to implement a bloom filter on a whiteboard off the top of my head to know when to use it.

	▲	Twirrim 3 hours ago \| parent [-]
		Hell, the number of times I've used a lot of the data structures that come up in leetcode exercises without at least looking at some reference material is pretty small. I usually assume I'm going to misremember it, and go double check before I write it so I don't waste ages debugging later.

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slopinthebag 5 hours ago | parent | prev [-]

Do you think they achieved that performance optimisation with a networked service because they switched from insertion sort to quicksort?

	▲	hparadiz 5 hours ago \| parent [-]
		I did the same thing in PHP before. Issue was a foreach over a foreach with a search. The fix was to build the result set as you populate the main array of objects. Basically as you add stuff to the array if there's a value that matches you throw it into another "results" array for any cardinality (unique value) that exists. Since in PHP objects are always just pointers your results arrays are relatively painless. Just a series of int32 integers basically. Then when you need an answer your result is instant. I ended up getting a 80-90% speed up. This is not just a php thing either. Folks end up doing this type of stuff in every language.