unordered_map

Initialization

• Empty Unordered Map:

std::unordered_map<int, std::string> myMap;  // Empty unordered_map

• brace initialization:

std::unordered_map<int, std::string> myMap = {
    {1, "one"},
    {2, "two"},
    {3, "three"}
};

Insert Elements

• Insert Single Element:

myMap[1] = "one";  // Insert key-value pair
// or
myMap.insert(std::make_pair(1, "one"));  // Insert key-value pair

Access Elements

• Access Value by Key:

std::string value = myMap[1];  // Access value by key, returns std::string

• Find Element:

auto it = myMap.find(1);
// Returns iterator to the element if key exists, otherwise returns myMap.end()
it->first  # key
it->second # value

Removing Elements

• Remove Element by Key:

myMap.erase(1);  // Removes element with key 1, returns number of elements removed (size_t)

Query Attributes

• Get Map Size:

size_t size = myMap.size();  // Returns the number of elements in the map (size_t)

• Check if Map is Empty:

bool isEmpty = myMap.empty();  // Returns true if the map is empty, otherwise false (bool)

Iterating through Unordered Map

• Using Iterator:

for (auto it = myMap.begin(); it != myMap.end(); ++it) {
    // it->first: key
    // it->second: value
}

• Using Range-based For Loop:

for (const auto& [key, value] : myMap) {
    // key: key
    // value: value
}

Other Common Operations

• Clear Map:

myMap.clear();  // Removes all elements from the map