# 5. Hashing Implementation with C++ STL

In C++, instead of creating a Hash Table manually, you could use **Standard Template Library (STL)**. The STL implementation **automatically** handles hash functions, collisions, and **rehashing** when the load factor gets too high.
    
## 5.1. `std::unordered_map` (Key-Value)

`std::unordered_map` is a Hash Map implementation for **Key-Value pairs**. The purpose of this template is to map Keys to Values. It acts like a **dictionary**, where you look up a word (key) to get its definition (value).
    
```cpp
#include <iostream>
#include <string>
#include <unordered_map>

int main() {
    // Key: string (name), Value: int (grade)
    std::unordered_map<std::string, int> studentGrades;

    studentGrades["Budi"] = 90;
    studentGrades["Ani"] = 85;

    // Access value using key
    std::cout << "Budi's Grade: " << studentGrades["Budi"] << std::endl;
}
```

## 5.2. `std::unordered_set` (Unique Keys)

`std::unordered_set` is a Hash Set implementation that only stores **unique keys**. This template is used to check whether a **key is on the list or not**, like a **guest book**.

```cpp
#include <iostream>
#include <string>
#include <unordered_set>

int main() {
    std::unordered_set<std::string> attendanceList;

    attendanceList.insert("Budi");
    attendanceList.insert("Ani");
    attendanceList.insert("Budi"); // Ignored, because "Budi" already exists

    // Check existence
    if (attendanceList.count("Budi") > 0) {
        std::cout << "Budi is present." << std::endl;
    }
}
```

## 5.3. Comparison: `map` vs. `set`

Aspect | `map` | `set`
:----: | :---: | :---:
**Feature** | `std::unordered_map<Key, Value>` | `std::unordered_map<Key>`
**What is Stored** | Key-Value pairs | Key only
**Element Type** | `std::pair<const Key, Value>` | `Key`
**Main Purpose** | Mapping Keys to Values | Storing unique Keys
**Data Access** | `map[key]` (get/set value) | `set.count(key)` (check existence)