For C++ STL containers such as vector and list, the complexity of finding elements and inserting or removing them is self-explanatory. However, for the map container, even though I know from my reading that the access and insertion complexity/performance is O(log(n)), I can't work out why. I clearly don't understand maps as much as I need to, so some enlightenment on this topic would be very much appreciated.
10
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have you seen this? stackoverflow.com/a/222674/1025391
– moooeeeep
2 Answers
12
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The elements of a map or set are contained in a tree structure; every time you examine a node of the tree, you determine if the element you're trying to find/insert is less than or greater than the node. The number of times you need to do this (for a properly balanced tree) is log2(N) because each comparison throws out half of the possibilities.
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As slavik262 points, maps are usually implemented with red-black-trees, which are self-balanced. Check the complexity of a red-black-tree for example in the wikipedia I don't know any implementation of a map with a binary tree; if Mark Ransom knows one, I'd be pleased to know which one.
