# JavaScript Recursion - Exercises, Practice, Solution

## JavaScript Recursion [13 exercises with solution]

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Use recursion to solve the following exercises.

**1. **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. **Write a JavaScript program to find the greatest common divisor (GCD) of two positive numbers using recursion.

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**3. **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. **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. **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.

8^{2} = 8 x 8 = 64. Here 8 is the base and 2 is the exponent.

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**6. **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. **Write a JavaScript program to check whether a number is even or not.

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**8. **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. **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. **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. **Write a JavaScript program to convert binary number (positive) to decimal number using recursion.

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**12. **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. **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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**More to Come ! **

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