Hash table

Introduction to Hash table

A Hash Table is a data structure that stores key-value pairs using a hash function to map keys to array indices for fast access.

Key Properties

• Key → Index using a hash function
• Fast Access: Average O(1) time for insert, search, delete
• Handles Collisions using chaining or open addressing
• Unordered data storage
• Used in dictionaries, caches, sets, etc.

Example in C++

#include <iostream>
#include <unordered_map>
using namespace std;

int main() {
    unordered_map<string, int> marks;

    marks["Alice"] = 90;
    marks["Bob"] = 80;

    cout << "Alice's marks: " << marks["Alice"] << endl;

    // Check if key exists
    if (marks.count("Bob"))
        cout << "Bob is present." << endl;

    return 0;
}

    

Learning resource

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