hashmap.cpp

#include <iostream>
#include <vector>
#include <string>
using namespace std;

// A simple hash map implementation using vector
class HashMap {
private:
    static const int SIZE = 100; // Size of the hash table
    vector<pair<string, int>> table[SIZE]; // Vector of pairs to handle collisions (chaining)

    // Hash function: Calculates the index for a given key
    int hashFunction(const string& key) {
        int hash = 0;
        for (char ch : key) {
            hash = (hash + ch) % SIZE;
        }
        return hash;
    }

public:
    // Insert a key-value pair into the hash map
    void insert(const string& key, int value) {
        int index = hashFunction(key);
        // Check if the key already exists and update the value if so
        for (auto& pair : table[index]) {
            if (pair.first == key) {
                pair.second = value;
                return;
            }
        }
        // Otherwise, add a new key-value pair
        table[index].push_back({key, value});
    }

    // Get the value associated with a key
    int get(const string& key) {
        int index = hashFunction(key);
        for (const auto& pair : table[index]) {
            if (pair.first == key) {
                return pair.second;
            }
        }
        throw runtime_error("Key not found");
    }

    // Check if a key exists in the hash map
    bool contains(const string& key) {
        int index = hashFunction(key);
        for (const auto& pair : table[index]) {
            if (pair.first == key) {
                return true;
            }
        }
        return false;
    }

    // Display the hash map content
    void display() {
        for (int i = 0; i < SIZE; i++) {
            if (!table[i].empty()) {
                cout << "Index " << i << ": ";
                for (const auto& pair : table[i]) {
                    cout << "[" << pair.first << ": " << pair.second << "] ";
                }
                cout << endl;
            }
        }
    }
};

int main() {
    HashMap map;

    // Insert some key-value pairs
    map.insert("apple", 3);
    map.insert("banana", 5);
    map.insert("cherry", 7);
    map.insert("date", 9);

    // Display the hash map
    cout << "HashMap contents:" << endl;
    map.display();

    // Get a value
    try {
        cout << "Value for 'apple': " << map.get("apple") << endl;
        cout << "Value for 'banana': " << map.get("banana") << endl;
    } catch (const exception& e) {
        cout << e.what() << endl;
    }

    // Check if a key exists
    cout << "Contains 'cherry': " << (map.contains("cherry") ? "Yes" : "No") << endl;
    cout << "Contains 'grape': " << (map.contains("grape") ? "Yes" : "No") << endl;

    return 0;
}