Recursion Base Case and Recursive Case in DSA Typescript - Build from Scratch

Recursion Base Case and Recursive Case

📖 Scenario: Imagine you have a stack of plates, and you want to count how many plates are in the stack by taking one plate off at a time until none are left.

🎯 Goal: You will build a simple recursive function in TypeScript that counts down from a number to zero using recursion. This will teach you how to set a base case and a recursive case.

📋 What You'll Learn

Create a variable called startNumber with the value 5.

Create a recursive function called countDown that takes a number parameter called num.

In countDown, write a base case that stops recursion when num is zero or less.

In the recursive case, print the current num and call countDown with num - 1.

Call countDown with startNumber.

Print each number on its own line.

💡 Why This Matters

🌍 Real World

Recursion is used in many places like searching files in folders, solving puzzles, and processing nested data.

💼 Career

Understanding recursion helps in writing clean code for problems that repeat themselves, which is common in software development and technical interviews.

1

Create the starting number

Create a variable called startNumber and set it to 5.

DSA Typescript

// Your code here

Hint

Use const startNumber = 5; to create the variable.

2

Define the recursive function

Create a function called countDown that takes a parameter num of type number.

DSA Typescript

const startNumber = 5;

// Define the countDown function here

Hint

Use function countDown(num: number): void { } to define the function.

3

Add base case and recursive case

Inside countDown, write a base case that returns when num is less than or equal to zero. Otherwise, print num and call countDown with num - 1.

DSA Typescript

const startNumber = 5;

function countDown(num: number): void {
  // Add base case and recursive case here
}

Hint

Use if (num <= 0) { return; } for the base case. Then print num and call countDown(num - 1).

4

Call the function and print output

Call countDown with startNumber to start the countdown.

DSA Typescript

const startNumber = 5;

function countDown(num: number): void {
  if (num <= 0) {
    return;
  }
  console.log(num);
  countDown(num - 1);
}

// Call countDown here

Hint

Use countDown(startNumber); to start the countdown.