Python Recursion Masterclass: Core Logic Building

DAY 9 – Python Revision | Recursion Masterclass (Core Logic Building) #Python #Recursion #LogicBuilding #FAANGPrep #DSA Recursion means a function calling itself until a base condition stops it. Ye technique har FAANG interview ka core hoti hai, specially: Tree problems Backtracking Divide & Conquer Dynamic Programming Aaj ke 4 powerful recursion problems 👇 (clean code + explanation) 🧩 Problem 1 — Factorial using Recursion (Base Concept) Input: 5 Output: 120 ✔ Recursion Logic Base case → n == 0 → return 1 Recursive case → n * factorial(n-1) def factorial(n): if n == 0: return 1 return n * factorial(n - 1) print(factorial(5)) Output: 120 🧩 Problem 2 — Fibonacci Using Recursion (Interview Favorite) Input: 6 Output: 8 ✔ Recursion Logic Fib(n) = Fib(n-1) + Fib(n-2) def fib(n): if n <= 1: return n return fib(n - 1) + fib(n - 2) print(fib(6)) Output: 8 🧩 Problem 3 — Sum of Digits Using Recursion (Logic Booster) Input: 1234 Output: 10 ✔ Recursion Logic Base → jab number 0 ho Recursive → last digit add + remaining digits ka sum def sum_of_digits(n): if n == 0: return 0 return (n % 10) + sum_of_digits(n // 10) print(sum_of_digits(1234)) Output: 10 🧩 Problem 4 — Reverse a String Using Recursion (Amazon) Input: "hello" Output: "olleh" ✔ Recursion Logic Base → length 0 or 1 Recursive → last char + reverse of remaining string def reverse_string(s): if len(s) <= 1: return s return reverse_string(s[1:]) + s[0] print(reverse_string("hello")) Output: olleh

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