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    <p>We know that the absolute best case runtime is O(m+n) this is due to the fact that you at least have to scan over all of the data in order to be able to merge the lists. Given this, your second method should give you that type of behavior. </p> <p>Have you profiled your second method to find out what the bottlenecks are? It is quite possible that, depending on the amount of data you are talking about it is actually impossible to do what you want in the specified amount of time. One way to verify this is to do something simple like sum up all the start and end values of the spans in each vector in a loop, and time that. Basically here you are doing a minimal amount of work for each element in the vectors. This will provide you with a baseline for the best performance you can expect to get.</p> <p>Beyond that you can avoid copying the vectors element by element by using the stl swap method, and you can preallocate the temp vector to a certain size in order to avoid triggering the expansion of the array when you are merging the elements.</p> <p>You might consider using 2 vectors in your system and whenever you need to do a merge you merge into the unused vector, and then swap (this is similar to double buffering used in graphics). This way you don't have to reallocate the vectors every time you do the merge.</p> <p>However, you are best off profiling first and finding out what your bottleneck is. If the allocations are minimal compared to the actual merging process than you need to figure out how to make that faster. </p> <p>Some possible additional speedups could come from accessing the vectors raw data directly which avoids the bounds checks on each access the data.</p>
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    1. POHelp with algorithm for merging vectors
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    1. COThanks for reminding me of std::swap, it might actually be the deal breaker. I'll be back after testing this out ;)
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