When to Use Hash Tables

Hash tables are a good choice in scenarios where you need fast lookups, insertions, and deletions based on a key. They provide constant-time O(1) average-case complexity for these operations, making them efficient for large datasets.

Consider using hash tables when:

1. You have a large amount of data and need to perform frequent lookups based on a unique key.
2. You want to associate values with keys and retrieve them quickly.
3. You don't need to maintain a specific order of elements.

For example, if you're building a phone book application where you want to store and retrieve contact information based on a person's name, a hash table would be a suitable choice. The name can serve as the key, and the associated contact details can be stored as the value.

1#include <iostream>
2#include <string>
3#include <unordered_map>
4
5int main() {
6  std::unordered_map<
7    std::string, std::string> phoneBook;
8
9  // Adding entries to the phone book
10  phoneBook["John"] = "123-456-7890";
11  phoneBook["Alice"] = "987-654-3210";
12
13  // Retrieving a phone number
14  std::string name = "John";
15  auto it = phoneBook.find(name);
16  if (it != phoneBook.end()) {
17    std::cout << "Phone number of " << name
18      << ": " << it->second << '\n';
19  } else {
20    std::cout << "Contact not found.\n";
21  }
22}

1Phone number of John: 123-456-7890

However, if you need to maintain a sorted order of elements or perform range queries, other data structures like balanced binary search trees (e.g., std::map) might be more appropriate.