Recursion Advance Problems - rohit120582sharma/Documentation GitHub Wiki

Reverse

Write a recursive function called reverse which accepts a string and returns a new string in reverse.

// Write a recursive function called Reverse which accepts a string and returns a new string in reverse.
function reverse(str){
	// Declare variables
	var length = str.length;

	// Base Case
	if(length <= 1) return str;

	// Change input and return
	var lastChar = str.charAt(length-1);
	var subStr = str.substr(0, (length - 1));

	// return
	return lastChar + reverse(subStr);
}
// reverse('awesome') // 'emosewa'
// reverse('rithmschool') // 'loohcsmhtir'

isPalindrome

Write a recursive function called isPalindrome which returns true if the string passed to it is a palindrome (reads the same forward and backward). Otherwise it returns false.

function isPalindrome(str){
	// Base case
	if(str.length <= 1) return true;
	if(str.length <= 2) return (str[0] === str[1]);

	// Change input and return
	if(str[0] === str.slice(-1)){
		return isPalindrome(str.slice(1,-1));
	}
	return false;
}
// isPalindrome('awesome') // false
// isPalindrome('foobar') // false
// isPalindrome('tacocat') // true
// isPalindrome('amanaplanacanalpanama') // true
// isPalindrome('amanaplanacanalpandemonium') // false

flattern

Write a recursive function called flatten which accepts an array of arrays and returns a new array with all values flattened.

function flatten(oldArr){
	// Create an return array
	var newArr = [];

	// Loop over an array
	for(var i=0; i<oldArr.length; i++){
		if(Array.isArray(oldArr[i])){
			newArr = newArr.concat(flatten(oldArr[i]));
		}else{
			newArr.push(oldArr[i]);
		}
	}

	// Return
	return newArr;
}
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