Recursion on Arrays and Strings in DSA Typescript - Build from Scratch

Sum of Array Elements Using Recursion

📖 Scenario: Imagine you have a list of daily expenses and you want to find out the total amount spent. Instead of adding them one by one using a loop, you will use a simple method called recursion to add all the numbers.

🎯 Goal: Build a TypeScript program that uses recursion to calculate the sum of all numbers in an array.

📋 What You'll Learn

Create an array called expenses with exact numbers: 100, 200, 300, 400, 500

Create a variable called length that stores the length of the expenses array

Write a recursive function called sumArray that takes the array and its length as parameters and returns the sum of the elements

Print the result of calling sumArray(expenses, length)

💡 Why This Matters

🌍 Real World

Recursion helps solve problems where a task can be broken down into smaller similar tasks, like calculating totals, searching, or sorting.

💼 Career

Understanding recursion is important for coding interviews and solving complex problems efficiently in software development.

1

Create the expenses array

Create an array called expenses with these exact numbers: 100, 200, 300, 400, 500

DSA Typescript

# Your code here

Hint

Use square brackets [] to create the array and separate numbers with commas.

2

Create the length variable

Create a variable called length that stores the length of the expenses array

DSA Typescript

const expenses: number[] = [100, 200, 300, 400, 500];
# Your code here

Hint

Use the length property of the array to get its size.

3

Write the recursive sumArray function

Write a recursive function called sumArray that takes two parameters: arr (an array of numbers) and n (a number). The function should return the sum of the first n elements of arr. Use the base case when n is 0 to return 0, otherwise return the last element plus the sum of the rest.

DSA Typescript

const expenses: number[] = [100, 200, 300, 400, 500];
const length: number = expenses.length;

# Your code here

Hint

Think of the function calling itself with one less element until it reaches zero.

4

Print the sum of the expenses array

Print the result of calling sumArray(expenses, length) using console.log

DSA Typescript

const expenses: number[] = [100, 200, 300, 400, 500];
const length: number = expenses.length;

function sumArray(arr: number[], n: number): number {
    if (n === 0) {
        return 0;
    } else {
        return arr[n - 1] + sumArray(arr, n - 1);
    }
}

# Your code here

Hint

Use console.log to show the final sum on the screen.