JavaScript Recursion - Exercises, Practice, Solution

JavaScript Recursion [13 exercises with solution]

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Use recursion to solve the following exercises.

1. Factorial Calculation

Write a JavaScript program to calculate the factorial of a number.  
In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. For example, 5! = 5 x 4 x 3 x 2 x 1 = 120
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2. GCD Using Recursion

Write a JavaScript program to find the greatest common divisor (GCD) of two positive numbers using recursion.  
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3. Range of Integers Using Recursion

Write a JavaScript program to get integers in the range (x, y) using recursion.  
Example : range(2, 9)
Expected Output : [3, 4, 5, 6, 7, 8]
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4. Sum of Array Elements

Write a JavaScript program to compute the sum of an array of integers.  
Example : var array = [1, 2, 3, 4, 5, 6]
Expected Output : 21
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5. Exponentiation

Write a JavaScript program to compute the exponent of a number.  
Note : The exponent of a number says how many times the base number is used as a factor.
8² = 8 x 8 = 64. Here 8 is the base and 2 is the exponent.
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6. Fibonacci Sequence

Write a JavaScript program to get the first n Fibonacci numbers.  
Note : The Fibonacci Sequence is the series of numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, . . . Each subsequent number is the sum of the previous two.
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7. Check Even or Odd

Write a JavaScript program to check whether a number is even or not.  
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8. Binary Search

Write a JavaScript program for binary search.  
Sample array : [0,1,2,3,4,5,6]
console.log(l.br_search(5)) will return '5'
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9. Merge Sort

Write a merge sort program in JavaScript.  
Sample array : [34,7,23,32,5,62]
Sample output : [5, 7, 23, 32, 34, 62]
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10. Recursive Palindrome Check

Write a JavaScript program to check whether a given string is a palindrome or not using recursion.  
A palindrome is a word, number, phrase, or other sequence of symbols that reads the same backwards as forwards, such as the words madam or racecar, the date/time stamps 11/11/11 11:11 and 02/02/2020, and the sentence: "A man, a plan, a canal - Panama".
Test Data:
("madam") -> true
("abdb") -> false
("ab") -> false
(test("a") -> true
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11. Binary to Decimal Conversion

Write a JavaScript program to convert binary number (positive) to decimal number using recursion.  
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12. Recursive Binary Search in Array

Write a JavaScript program to search for a given integer in an array of sorted integers using the Binary Search Algorithm and recursion.  
Test Data:
([1, 2, 3, 5, 6, 7, 10, 11, 14, 15, 17, 19, 20, 22, 23], 6) -> 4
([1, 2, 3, 5, 6, 7, 10, 11, 14, 15, 17, 19, 20, 22, 23], 16) -> -1
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13. Letter Combinations from Digits

A string consists of digits ranging from 2 to 9, inclusive. Write a JavaScript program to get all possible letter combinations that represent the number using recursion.  
Test Data:
("12") -> ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
("9") -> ["y", "z"]
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