What is an Unordered_map?

At its core, std::unordered_map is an associative container that maps unique keys to values using a hash table data structure. Unlike its counterpart std::map, which maintains elements in sorted order, std::unordered_map eshews ordering constraints, offering constant-time average complexity for key operations.

In simple terms:

Imagine you have a notebook where you want to keep track of information, but instead of writing everything down in order, you want to quickly find each piece of information based on a unique key. That's what an unordered_map is like in C++.

Here's how it works:

1. Key-Value Pairs: Each piece of information you want to store is called a "value", and you associate it with a unique "key". For example, you might have a key like "Name" and its associated value might be "John".
2. Fast Lookup: Just like how you'd flip through your notebook to find information quickly based on the section headers or tabs, an unordered_map lets you find information super fast based on its unique key.
3. No Specific Order: The entries in your notebook are not necessarily in any particular order. You might have "Age" written down before "Name" or vice versa. Similarly, in an unordered_map, the key-value pairs are not sorted in any specific order.
4. Avoid Duplicate Keys: Each key in the map must be unique. If you try to add a new key that's the same as an existing one, it won't work - it's like trying to add another tab with the same name in your notebook.

Syntax

In order to use an unordered_map in C++, we first need to include the unordered_map header file.

#include <unordered_map>

int main() {
    std::unordered_map<KeyType, ValueType> myMap;
    // Add key-value pairs, perform operations
    return 0;
}

In this syntax:

• KeyType represents the type of keys you want to use.
• ValueType represents the type of values associated with each key.
• myMap is the name of the unordered_map variable you are declaring.

Example:

unordered_map<int, int> unordered_map_integer;

Initializing: