DSA — HashMap

What is a HashMap?

A hash table implementation that stores key-value pairs.

# Python dict is a HashMap
 hashmap = {}
 hashmap["name"] = "John"
 hashmap["age"] = 30

# Using dict constructor
hashmap = dict(name="John", age=30)

Common Operations

# Insert/Update
hashmap["key"] = "value"

# Access
value = hashmap["key"]

# Safe access
value = hashmap.get("key", "default")

# Delete
del hashmap["key"]
hashmap.pop("key")

# Check existence
"key" in hashmap

# Get all keys/values
hashmap.keys()
hashmap.values()
hashmap.items()

Use Cases

Use Case	Example
Counting	Character frequency
Caching	LRU cache
Indexing	Database indexing
Grouping	Group by category

Counting Pattern

def count_words(text):
    words = text.lower().split()
    freq = {}
    for word in words:
        freq[word] = freq.get(word, 0) + 1
    return freq

Mini Practice

1. Count character frequencies
2. Group items by category
3. Implement a cache
4. Find duplicates efficiently

Up Next

Continue with Sets — set data structure.