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C++ map 和 hashmap 区别

c++容器 sql 数据结构

1. stl map is an associative array where keys are stored in sorted order using balanced trees. while hash_map is a hashed associated container, where keys are not stored in an ordered way. key, value pair is stored using a hashed function. 2. insertion and lookup takes ologn time in map, also performance would degrade as the key size increases. mainly balance operations on large key ranges would kill performance. while lookup is very efficient o(1) in hash_map. 3. map is useful where you want to store keys in sorted order, hash_map is used where keys order is not important and lookup is very efficient. 4. one more difference is map has the important property that inserting a new element into a map does not invalidate iterators that point to existing elements. erasing an element from a map also does not invalidate any iterators. performance would mostly be o(lgn) due to the implementation of a balanced tree. for map custom objects you would need at the minimum the following operators to store data in a map "<" ">" "==" and of course the other stuff for deep copy.

2020-06-07

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js & array & shuffle

https 网络安全 java javascript

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

2020-06-07

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