# unordered\_map

***

**1. Implementing a Key-Value Cache**

```cpp
#include <unordered_map>

class KVCache {
public:
    void put(const string& key, const string& value) { cache[key] = value; }
    string get(const string& key) { return cache[key]; }
private:
    unordered_map<string, string> cache;
};
```

**2. Counting Occurrences of Words in Text**

```cpp
#include <unordered_map>

unordered_map<string, int> word_counts;
for (const string& word : words) {
    word_counts[word]++;
}
```

**3. Grouping Items by Category**

```cpp
#include <unordered_map>

unordered_map<string, vector<string>> items_by_category;
for (const string& item : items) {
    items_by_category[category(item)].push_back(item);
}
```

**4. Creating a Graph Data Structure**

```cpp
#include <unordered_map>

unordered_map<int, vector<int>> graph;
```

**5. Implementing a Dictionary**

```cpp
#include <unordered_map>

unordered_map<string, string> dictionary;
string translation = dictionary["word"];
```

**6. Storing User Preferences**

```cpp
#include <unordered_map>

unordered_map<string, string> user_preferences;
string preference = user_preferences["username"];
```

**7. Caching Database Queries**

```cpp
#include <unordered_map>

unordered_map<string, string> query_cache;
string result = query_cache[query];
```

**8. Representing Sparse Matrices**

```cpp
#include <unordered_map>

unordered_map<pair<int, int>, double> sparse_matrix;
double value = sparse_matrix[{i, j}];
```

**9. Creating a Set of Unique Elements**

```cpp
#include <unordered_map>

unordered_map<int, bool> unique_elements;
if (unique_elements[element]) {
    // Element is already in the set
}
```

**10. Implementing a Bloom Filter**

```cpp
#include <unordered_map>

unordered_map<int, bool> bloom_filter;
```

**11. Tracking Objects in a Game**

```cpp
#include <unordered_map>

unordered_map<int, GameObject*> game_objects;
GameObject* player = game_objects[player_id];
```

**12. Creating a Lookup Table**

```cpp
#include <unordered_map>

unordered_map<string, int> lookup_table;
int value = lookup_table["key"];
```

**13. Representing a Trie Data Structure**

```cpp
#include <unordered_map>

unordered_map<char, TrieNode*> trie;
```

**14. Implementing a Hash Table**

```cpp
#include <unordered_map>

unordered_map<int, string> hash_table;
```

**15. Storing Metadata for File Paths**

```cpp
#include <unordered_map>

unordered_map<string, FileMetadata> file_metadata;
FileMetadata metadata = file_metadata["path"];
```

**16. Representing a Data Dictionary**

```cpp
#include <unordered_map>

unordered_map<string, DataColumn> data_dictionary;
```

**17. Implementing a Symbol Table for a Compiler**

```cpp
#include <unordered_map>

unordered_map<string, Symbol> symbol_table;
```

**18. Tracking Connections in a Network**

```cpp
#include <unordered_map>

unordered_map<int, vector<int>> connections;
```

**19. Representing a Directed Graph**

```cpp
#include <unordered_map>

unordered_map<int, vector<int>> directed_graph;
```

**20. Creating a Custom Index for a Database**

```cpp
#include <unordered_map>

unordered_map<string, vector<int>> custom_index;
```

**21. Storing User Session Data**

```cpp
#include <unordered_map>

unordered_map<string, SessionData> session_data;
```

**22. Tracking Recent Activity in an Application**

```cpp
#include <unordered_map>

unordered_map<string, Timestamp> recent_activity;
```

**23. Implementing a LRU Cache**

```cpp
#include <unordered_map>

unordered_map<int, pair<int, int>> lru_cache;
```

**24. Representing a Sparse Vector**

```cpp
#include <unordered_map>

unordered_map<int, double> sparse_vector;
```

**25. Tracking Progress in a Game**

```cpp
#include <unordered_map>

unordered_map<string, int> game_progress;
```

**26. Storing Configuration Settings**

```cpp
#include <unordered_map>

unordered_map<string, string> config_settings;
```

**27. Representing a Sudoku Puzzle**

```cpp
#include <unordered_map>

unordered_map<pair<int, int>, int> sudoku_puzzle;
```

**28. Creating a Calendar**

```cpp
#include <unordered_map>

unordered_map<Date, vector<Event>> calendar;
```

**29. Tracking User Rankings**

```cpp
#include <unordered_map>

unordered_map<string, int> user_rankings;
```

**30. Representing a Map of Locations**

```cpp
#include <unordered_map>

unordered_map<string, Location> map_of_locations;
```

**31. Creating a File System**

```cpp
#include <unordered_map>

unordered_map<string, File> file_system;
```

**32. Representing a Social Network**

```cpp
#include <unordered_map>

unordered_map<int, vector<int>> social_network;
```

**33. Implementing a Custom Data Type**

```cpp
#include <unordered_map>

struct CustomDataType

```