📘 Introduction to Arrays

🧠 What is an Array?

An array is a linear data structure that stores a fixed-size sequence of elements of the same type in contiguous memory locations. Arrays allow efficient random access via indexing and are foundational in many algorithmic solutions.

🛠️ Array Basics

✅ Declaration and Initialization 

arr = [10, 20, 30, 40]

✅ Accessing Elements 

print(arr[0])  # Output: 10

✅ Updating Elements 

arr[2] = 99

⚙️ Basic Array Operations

Operation Time Complexity
Access by index \(O(1)\)
Update by index \(O(1)\)
Insert at end \(O(1)\) (amortized for dynamic arrays)
Insert at index \(O(n)\)
Delete by index \(O(n)\)
Search (linear) \(O(n)\)

🔍 Understanding Memory Layout

Arrays are stored in contiguous blocks in memory, enabling constant-time access using the index:

arr[3] → Base Address + 3 × Size_of_Element

👉 This is why arrays are faster than linked lists for indexed access.

📊 Types of Arrays

  • 1D Array: Single row of elements — arr[5]
  • 2D Array: Matrix/grid — matrix[3][3]
  • Multidimensional Arrays: Arrays within arrays

🧪 Example Problems

🔹 Problem 1: Find Maximum Element in an Array 

arr = [2, 5, 1, 9, 3]
max_val = arr[0]
for num in arr:
    if num > max_val:
        max_val = num
print(max_val)

🔹 Problem 2: Reverse an Array In-Place 

arr = [1, 2, 3, 4, 5]
start = 0
end = len(arr) - 1
while start < end:
    arr[start], arr[end] = arr[end], arr[start]
    start += 1
    end -= 1
print(arr)

✍️ Practice Assignments

  1. Write a program to calculate the sum and average of elements in an array.

  2. Find the second largest element in an array.

  3. Implement a program to remove all negative numbers from an array.

  4. Practice accessing and updating values in a 2D array.

🔔 Next : We’ll dive into array problem-solving patterns like prefix sums, two-pointer technique, and sliding window.

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