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Learn Data Structures and Algorithms in C++

Basic Operations in Hash Table

Explore the fundamental operations of hash tables in C++ including insertion, search, and deletion. Understand how std::unordered_map facilitates these operations efficiently, and learn the differences between methods like [], insert(), and erase(). Discover a simplified implementation for core concept clarity while recognizing practical limitations and collision challenges.

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After understanding what a hash table is and how a hash function works, the next step is to study the three fundamental operations that make hash tables useful in practice: insertion, search, and deletion. These operations allow data to be stored, retrieved, and removed efficiently using a key.

In a hash table, each operation begins in the same way: the key is passed through the hash function to compute an index in the underlying array. Once that index is known, the table can access the corresponding location directly.

Hash table operations in C++

In C++, the std::unordered_map class from the <unordered_map> header provides a ready-to-use hash table implementation. You do not need to build one from scratch for most DSA problems. The following sections cover the three fundamental operations using std::unordered_map.

  1. Insertion

  2. Searching

  3. Deletion

Setting up an unordered_map

C++
#include <iostream>
#include <unordered_map>
#include <string>
int main() {
    // Create an unordered_map with string keys and int values
    std::unordered_map<std::string, int> table;
    return 0;
}
Setting up an unordered_map

Each key-value pair is stored in the map. The keys must be unique; inserting a key that already exists will overwrite its value.

The insertion operation

The insertion operation adds a new key-value pair to the hash table. If the key already exists, its value is updated. ...