AppDividend — C++ Unordered_map Example Unordered_map In C++ from appdividend.tumblr.com
Introduction
C++ is a popular programming language that has been in use for several decades. It provides developers with the tools to create efficient and powerful applications. One of the data structures that C++ provides is the unordered_map. This data structure is a container that stores elements in an unordered way. In this article, we will explore the usage of unordered_map in C++.
What is Unordered_Map?
An unordered_map is a container that stores elements using a hash table. It provides constant time access to its elements. The elements in an unordered_map are stored in an unordered way, which means that the order in which they are stored is not important. The unordered_map is part of the C++ Standard Template Library (STL).
How to Use Unordered_Map in C++
To use unordered_map in C++, you need to include the header file. Here is an example of how to declare an unordered_map:
std::unordered_map myMap;
In this example, we have declared an unordered_map that stores string keys and integer values. We can add elements to the unordered_map using the insert() function:
myMap.insert(std::make_pair("key1", 1));
Here, we have added an element to the unordered_map with the key "key1" and the value 1. We can also access the elements in the unordered_map using the [] operator:
int value = myMap["key1"];
This will retrieve the value associated with the key "key1".
Advantages of Unordered_Map
One of the advantages of unordered_map is its constant time access to elements. This means that the time it takes to access an element in the unordered_map does not depend on the size of the map. Another advantage is its ability to store elements in an unordered way, which makes it useful for applications where the order of elements is not important.
FAQ
What is the difference between unordered_map and map?
The main difference between unordered_map and map is the way they store their elements. Map stores its elements in a sorted order, while unordered_map stores its elements in an unordered way. Map provides logarithmic time access to its elements, while unordered_map provides constant time access.
When should I use unordered_map?
Unordered_map is useful in applications where the order of elements is not important, and constant time access to elements is required. It is also useful in applications where the size of the container may change frequently.
What is the worst-case time complexity of unordered_map?
The worst-case time complexity of unordered_map is O(n), where n is the number of elements in the container. This occurs when all elements are in the same bucket and a linear search is required to access an element.
Conclusion
Unordered_map is a useful data structure in C++ that provides constant time access to elements. It is a container that stores elements in an unordered way, which makes it useful in applications where the order of elements is not important. We hope this article has provided you with valuable information on the usage of unordered_map in C++.
