The ultimate guide to recursion interviews in JavaScript. Developed by FAANG engineers. Practice with real-world interview questions and get interview-ready in just a few hours.

If you’ve ever struggled with solving problems using recursion, or if you have to brush up your skills for an interview, this course is for you.

We'll start with the basics of what recursion is and why it’s important before diving into practicing solving actual questions. You’ll have access to detailed explanations and visualizations for each problem to help you along the way. 

By the time you have completed this course, you’ll be able to use all the concepts to solve complex real-world problems. We hope that through practicing recursion, you will be able to ace all recursion related questions in interviews at top tech companies.

Recursion for Coding Interviews in JavaScript

```javascript
 if (startIndex >= length) {
    return
  }
```

```javascript
if (startIndex <= length) {
 return
}
```

```javascript
if (startIndex >= length/2) {
   return
}
```

```javascript
if (startIndex >= 0) {
   return
}
```

The function below prints a string recursively, meaning that one character is printed in each recursive call.
```javascript
function printArray(array, startIndex, length) {
  // Base case
 ____________________________________
  
  console.log(array[startIndex] + "\t")
  
  // Recursively calling printArray to print next element in the array
  printArray(array, startIndex + 1, length)
}
```
What should the base case of the following code be?

The function below prints a string recursively, meaning that one character is printed in each recursive call.
<pre><code class="language-javascript">function printArray(array, startIndex, length) {
 // Base case
 ____________________________________
 
 console.log(array[startIndex] + &quot;\t&quot;)
 
 // Recursively calling printArray to print next element in the array
 printArray(array, startIndex + 1, length)
}
</code></pre>
What should the base case of the following code be?

```javascript
else {
	return array[0] + arraySum(array.slice(1))
}
```

```javascript
else {
	return (array[0], arraySum(array))
}
```

The function below prints the **sum** of all array elements using recursion.
```javascript
function arraySum(array) {
    // Base Case
    if (array.length == 0) {
        return 0
    }

    // Recursive Case    
    _______________________________________
}
```

What should the **recursive case** of the following code be?


The function below prints the sum of all array elements using recursion.
<pre><code class="language-javascript">function arraySum(array) {
 // Base Case
 if (array.length == 0) {
 return 0
 }

 // Recursive Case 
 _______________________________________
}
</code></pre>
What should the recursive case of the following code be?

Multiplies all the elements of the array.

What does the following function do:
```javascript
function foo(array) {
  // Base case
	if (array.length === 0) {
    return 1;
  }
  
  // Recursive case
	return array.shift() * foo(array);
}

// Driver Code
console.log(foo([1, 2, 3]))
 ```

What does the following function do:
<pre><code class="language-javascript">function foo(array) {
 // Base case
	if (array.length === 0) {
 return 1;
 }
 
 // Recursive case
	return array.shift() * foo(array);
}

// Driver Code
console.log(foo([1, 2, 3]))
</code></pre>

```javascript
if (middle > key) {
    return binarySearch(array(0, middleIndex), key);
} 
      
else {
    return binarySearch(array(middleIndex, length), key);
}
```

```javascript
return binarySearch(array.slice(middleIndex, length), key);
```

```javascript
if (middle > key) {
    return binarySearch(array.slice(0, middleIndex), key);
} 
else {
    return binarySearch(array.slice(middleIndex, length), key);
}
```

```javascript
 return binarySearch(array.slice(0, middleIndex), key);
```

Complete the following code for **binary search** in an array.
```javascript
function binarySearch (array, key) {
    var length = array.length;
    var middleIndex = Math.floor(length / 2);
    var middle = array[middleIndex];

    // Base case --> key is found
    if (middle === key) {
        return middleIndex; // Index at which the key is found
    }
  
   // Recursive case
    if (length > 1) {
        _________________________________________________________
    }
  
    return -1;
}

// Driver Code
var myArray = [1, 2, 3, 4, 5, 6];
var key = 4;
console.log(binarySearch(myArray, key));
```

Complete the following code for binary search in an array.
<pre><code class="language-javascript">function binarySearch (array, key) {
 var length = array.length;
 var middleIndex = Math.floor(length / 2);
 var middle = array[middleIndex];

 // Base case --&gt; key is found
 if (middle === key) {
 return middleIndex; // Index at which the key is found
 }
 
 // Recursive case
 if (length &gt; 1) {
 _________________________________________________________
 }
 
 return -1;
}

// Driver Code
var myArray = [1, 2, 3, 4, 5, 6];
var key = 4;
console.log(binarySearch(myArray, key));
</code></pre>

This Quiz will take approximately 10 minutes.

This Quiz will take approximately 10 minutes.

---
In the next chapter, we will use recursion to solve problems with data structures.

Recursion Fundamentals

Iteration Vs Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Test Your Knowledge 5

Quiz