std::unordered_map
suggest changeUsing std::unordered map
Introduction
std::unordered_map
is an associative container. It works on keys and their maps. Key as the names goes, helps to have uniqueness in the map. While the mapped value is just a content that is associated with the key. The data types of this key and map can be any of the predefined data type or user-defined.
Remarks
As the name goes, the elements in unordered map are not stored in sorted sequence. They are stored according to their hash values and hence, usage of unordered map has many benefits such as it only takes O(1) to search any item from it. It is also faster than other map containers. It is also visible from the example that it is very easy to implement as the operator ( []
) helps us to directly access the mapped value.
Declaration and usage
As already mentioned you can declare an unordered map of any type. Let’s have a unordered map named first with string and integer type.
unordered_map<string, int> first; //declaration of the map
first["One"] = 1; // [] operator used to insert the value
first["Two"] = 2;
first["Three"] = 3;
first["Four"] = 4;
first["Five"] = 5;
pair <string,int> bar = make_pair("Nine", 9); //make a pair of same type
first.insert(bar); //can also use insert to feed the values
Some basic methods
unordered_map<data_type, data_type> variable_name; //declaration
variable_name[key_value] = mapped_value; //inserting values
variable_name.find(key_value); //returns iterator to the key value
variable_name.begin(); // iterator to the first element
variable_name.end(); // iterator to the last + 1 element