Data Structure Algorithms

DATA STRUCTURES & ALGORITHMS

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Introduction to DSA & Arrays

What is DSA?

Data Structures and Algorithms (DSA) help you organize data and solve problems efficiently.

• Data Structure: How data is stored (Arrays, Linked List, Trees)
• Algorithm: Step-by-step solution to a problem

Why Learn DSA?

• Improves problem-solving skills
• Helps write faster code
• Important for interviews
• Used in real-world apps

Time & Space Complexity

Time Complexity

Complexity	Example	Meaning
O(1)	Access element	Constant
O(n)	Loop	Linear
O(n²)	Nested loops	Quadratic
O(log n)	Binary Search	Logarithmic

Space Complexity

arr = [1,2,3,4]  # O(n)

Arrays in Python

1D Array

arr = [10, 20, 30, 40]

2D Array

matrix = [
 [1,2],
 [3,4]
]

Operations

Traversal

for i in arr:
    print(i)

Insertion

arr.append(40)

Deletion

arr.remove(20)

Search

if 30 in arr:
    print("Found")

Strings in Python

What is String?

name = "Prem"
message = "Hello"

Strings are immutable.

Indexing

text = "Python"
print(text[0])
print(text[-1])

Slicing

print(text[0:3])
print(text[::-1])

String Methods

split()

"I love Python".split()

join()

" ".join(['I','love','Python'])

replace()

"I love Java".replace("Java","Python")

Logic Problems

Palindrome

text = "madam"
print(text == text[::-1])

Anagram

print(sorted("listen") == sorted("silent"))

Practice Problems

1. Count Vowels

text = input().lower()
vowels = "aeiou"

v = c = 0
for ch in text:
if ch.isalpha():
if ch in vowels:
v+=1
else:
c+=1

print(v, c)

2. Longest Word

sentence = input()
print(max(sentence.split(), key=len))

3. Reverse Words

sentence = input()
print(" ".join(sentence.split()[::-1]))

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