Map in C++ STL

Maps are associative containers that store key–value pairs in sorted order using a self-balancing Red-Black Tree. They provide efficient O(log n) time complexity for insertion, deletion, and searching operations.

• Maps do not allow duplicate keys.
• They support ordered traversal and functions like upper_bound() and lower_bound().

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Explanation: Above program demonstrates how to create and initialize a map in C++ using key–value pairs. It then iterates through the map using a range-based loop and prints each key along with its corresponding value.

Syntax

The map container is defined as std::map class templateinside the <map> header file.

map<key_type, value_type> m;

where,

• key_type: Data type of key.
• value_type: Data type of value.
• m: Name assigned to map.

Basic Operations

Basic operations on map containers are shown below:

1. Inserting Elements

• The insert() operation adds a new key-value pair to the map only if the key is not already present.
• If the key exists, insert() does not update the value and leaves the map unchanged.
• Time complexity to insert is O(log n).

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2. Accessing Elements

• We can access elements with [] operator which returns the value for a given key and inserts the key with a default value if it doesn't exist.
• To check if a key exists without adding it by we can use find().
• Time complexity to access elements by key is O(log n).

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3. Updating Elements

• To update a value, we can simply assign a new value to an existing key using map[key]= newValue; If the key already exists , the value gets updated.
• Time complexity to update element by key O(log n).

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4. Finding Elements

• find() function is used to check if key exists in a map which looks for key and returns its position if found.
• If key is not present in the map, find() returns a special value called end(), meaning not found.
• Time complexity to find element by key is O(log n).

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5. Traversing

• Loops can be used to traverse all key-value pairs in a map, which visits each pair in order sorted by the keys.
• Time complexity to traverse in a map is O(n).

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6. Deleting Elements

• To delete a key and its value from map use erase(key), which deletes the pair if the key exists, else does nothing.
• Time complexity to delete an element by key O(log n).