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Jul 11, 2009 · What are the requirements on a class that is to be used as the key? The map needs to be able to tell whether one key's value is less than another key's value: by default this means that (key1 < key2) must be a valid boolean expression, i.e. that the key type should implement the 'less than' operator.
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Rationale
One idea to have a map with two keys is to hold two mapsinternally. One that maps the first key to the second key, and the other one that maps the second key to the value. An insertion into the double-key map actually inserts two associations in the internal maps: Then a lookup on key1 one does two lookups internally: first finding the corresponding key2 to key1, and then finding the value corresponding to key2. And a lookup on key2 does only one lookup on the second map to find the correspon...
Code
Here is the code corresponding to the above rationale:
Discussion
This solution has the following drawbacks: 1. it doesn’t follow the conventions of the STL (no begin, end, find, operatornor aliases), which is bad because it isn’t compatible with STL algorithms, 2. the lookup of the first key takes more time that the lookup of the second one, although both are in log(N).
Let’s make this a collaborative exploration! Implement your own solution and link to it in a comment below. To submit your own solution about how to implement the double-key map, you can get started with this Godbolt template. It contains a couple of basic test cases that the structure should satisfy, but feel free to adapt them to your interface t...
Nov 24, 2023 · std::map is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare. Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as Red–black trees.
Mar 5, 2024 · In C++, a map is a container that stores elements in key-value pairs, where each key is unique and associated with a value. In this article, we will learn how to add multiple key-value pairs to a map in C++. Example: Input: . myMap = { {1, "one"} }; Elements to be insert = { {2, "two"}, {3, "three"}} Output: .
Jan 31, 2022 · A MultiKeyMap is a map that offers support for multiple keys. It is exactly the same as a normal map, except that it needs a container to store multiple keys. A simple solution to implement a MultiKeyMap in C++ is using std::pair for the key.
Apr 30, 2020 · Multidimensional map s are used when we want to map a value to a combination of keys. The key can be of any data type, including those that are user-defined. Multidimensional maps are nested maps; that is, they map a key to another map, which itself stores combinations of key values with corresponding mapped values. Syntax:
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Oct 30, 2023 · Map in C++ Standard Template Library (STL) - GeeksforGeeks. Last Updated : 30 Oct, 2023. Maps are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have the same key values.
