CS101-LC03 — Python for Interviews

🎯 Why Python Matters in Interviews

Python is not just a language.
It is a thinking tool.

Interviewers use Python to test:

• Clarity of thought
• Data structure mastery
• Algorithmic intuition
• Code readability

🧠 Core Python Philosophy

Simple is better than complex.
Readability counts.

If your code is easy to read, it is easy to debug and scale.

🔁 Iteration Patterns (Fundamental)

Looping Over Values

for x in arr:
    print(x)

Looping With Index

for i, x in enumerate(arr):
    print(i, x)

Looping in Reverse

for x in reversed(arr):
    print(x)

🧺 Containers in Python

List (Ordered, Mutable)

nums = [1, 2, 3]
nums.append(4)

Use when:

• Order matters
• Frequent appends

Tuple (Ordered, Immutable)

point = (3, 4)

Use when:

• Data should not change
• Hashable keys

Set (Unique Elements)

seen = set()
seen.add(1)

Use when:

• Deduplication
• Fast membership test

⏱️ Average lookup: O(1)

Dictionary (Key → Value)

freq = {}
for x in arr:
    freq[x] = freq.get(x, 0) + 1

Use when:

• Counting
• Mapping
• Fast lookup

🔍 Searching Patterns

Linear Search

def linear_search(arr, target):
    for x in arr:
        if x == target:
            return True
    return False

⏱️ O(n)

Binary Search (Sorted Array)

def binary_search(arr, target):
    l, r = 0, len(arr) - 1

    while l <= r:
        mid = (l + r) // 2
        if arr[mid] == target:
            return True
        elif arr[mid] < target:
            l = mid + 1
        else:
            r = mid - 1

    return False

⏱️ O(log n)

🧮 Vector Operations (AI Foundation)

Vector Addition

def add_vectors(a, b):
    return [a[i] + b[i] for i in range(len(a))]

Dot Product

def dot(a, b):
    return sum(a[i] * b[i] for i in range(len(a)))

Used in:

• Neural networks
• Similarity
• Attention

🧱 Matrix Basics (2D Lists)

matrix = [
    [1, 2, 3],
    [4, 5, 6]
]

Matrix Traversal

for row in matrix:
    for val in row:
        print(val)

Matrix Multiplication (Interview Classic)

def matmul(A, B):
    result = [[0]*len(B[0]) for _ in range(len(A))]

    for i in range(len(A)):
        for j in range(len(B[0])):
            for k in range(len(B)):
                result[i][j] += A[i][k] * B[k][j]

    return result

⏱️ O(n³)

🧠 Functions & Clean Design

def square(x: int) -> int:
    return x * x

Why types help:

• Clarity
• Debugging
• Documentation

🧱 Classes & Objects (VERY IMPORTANT)

Defining a Class

class Vector:
    def __init__(self, values):
        self.values = values

    def dot(self, other):
        return sum(a*b for a, b in zip(self.values, other.values))

Using the Class

v1 = Vector([1, 2, 3])
v2 = Vector([4, 5, 6])
print(v1.dot(v2))

🧬 Inheritance (Interview Favorite)

class Matrix(Vector):
    def shape(self):
        return (len(self.values), len(self.values[0]))

Why inheritance matters:

• Code reuse
• Abstraction
• Design thinking

🧠 Pythonic Tricks Interviewers Love

List Comprehension

squares = [x*x for x in range(10)]

Dictionary Comprehension

freq = {x: arr.count(x) for x in arr}

Any / All

any(x > 0 for x in arr)
all(x > 0 for x in arr)

🚨 Common Interview Mistakes

❌ Overcomplicating ❌ Ignoring edge cases ❌ Forgetting time complexity ❌ Writing unreadable code

🏁 Final Interview Advice

Python interviews are not about syntax. They are about how you think.

If you master:

• Containers
• Loops
• Functions
• Classes
• Vectors & matrices

You are interview-ready.

🎉 Congratulations

This chapter alone covers:

• CS fundamentals
• LeetCode readiness
• AI mathematical intuition
• Clean software design

You’re officially dangerous now 😄🔥