5.3: Student Activity – Recursion & Lambda Challenge Pack

📦 Practice building recursive functions and using lambda expressions for quick tasks!

---

🎯 Objective:

By the end of this activity, you'll be able to:

• Define and use recursive functions with base cases
• Create and use lambda functions with map(), filter(), and sorted()
• Solve real problems with short, reusable function logic

---

🧱 Part 1: Recursion Practice

1️⃣ Sum of Numbers 1 to N

Write a recursive function that returns the sum from 1 to n.

def sum_to_n(n):
    if n <= 0:
        return 0
    else:
        return n + sum_to_n(n - 1)

print("Sum to 5:", sum_to_n(5))  # Output: 15

✅ Test with sum_to_n(10), sum_to_n(1), and sum_to_n(0).

---

2️⃣ Recursive Factorial

def factorial(n):
    if n <= 1:
        return 1
    return n * factorial(n - 1)

print("5! =", factorial(5))  # Output: 120

✅ Test with factorial(0), factorial(3), and factorial(7).

---

3️⃣ Fibonacci Sequence

def fibonacci(n):
    if n <= 1:
        return n
    return fibonacci(n - 1) + fibonacci(n - 2)

print("Fibonacci of 5:", fibonacci(5))  # Output: 5

✅ Try with small numbers only (e.g., fibonacci(6)) — larger values get slow.

---

⚡ Part 2: Lambda Function Practice

4️⃣ Square a List with map() + lambda

nums = [1, 2, 3, 4, 5]
squares = list(map(lambda x: x * x, nums))
print("Squares:", squares)  # [1, 4, 9, 16, 25]

---

5️⃣ Filter Even Numbers with filter() + lambda

numbers = list(range(20))
evens = list(filter(lambda x: x % 2 == 0, numbers))
print("Evens:", evens)  # [0, 2, 4, ..., 18]

---

6️⃣ Sort Names by Last Letter with sorted() + lambda

names = ["Alice", "Bob", "Charlie", "Zoe"]
sorted_names = sorted(names, key=lambda name: name[-1])
print("Sorted by last letter:", sorted_names)

---

🧠 Bonus Challenge

7️⃣ Recursive Palindrome Checker

Write a recursive function that checks whether a word is a palindrome (reads the same backward).

def is_palindrome(word):
    if len(word) <= 1:
        return True
    if word[0] != word[-1]:
        return False
    return is_palindrome(word[1:-1])

print(is_palindrome("racecar"))  # True
print(is_palindrome("python"))   # False

---

8️⃣ Lambda to Capitalize All Names

names = ["alice", "bob", "carla"]
capitalized = list(map(lambda s: s.capitalize(), names))
print("Capitalized:", capitalized)  # ['Alice', 'Bob', 'Carla']

---

✅ What to Submit:

• Your complete script with all 8 parts
• Test output from several examples
• (Bonus if attempted) Your palindrome checker or your own lambda + recursion idea

---

📝 Learning Check

Task	✅
Created and tested recursive functions
Used base case + recursive step correctly
Used map(), filter(), or sorted()
Wrote at least 2 lambda expressions
Tested code and printed clear results