Notes

https://www.softwaretestinghelp.com/coding-interview-questions/
extra --> https://www.programiz.com/javascript/examples/check-occurrence-string

-->Reverse a String With Built-In Functions
1st method
function reverseString(str){
var splitString = str.split("");
console.log("splitString",splitString)

var reverseString = splitString.reverse();
console.log(reverseString,"reverseString")

var joinString = reverseString.join("");
console.log(joinString,"joinString")

return joinString;
}

var a = reverseString("hello! how are you");
console.log(a,'ok')

2nd method :
function reverseString(str){
var splitString = str.split("").reverse().join("");

return splitString;
}
var a = reverseString("hello! how are you");
console.log(a,'ok')

--> Reverse a String With a Decrementing For Loop
function reverseString(str) {
// Step 1. Create an empty string that will host the new created string
var newString = "";

// Step 2. Create the FOR loop
/* The starting point of the loop will be (str.length - 1) which corresponds to the
last character of the string, "o"
As long as i is greater than or equals 0, the loop will go on
We decrement i after each iteration */
for (var i = str.length - 1; i >= 0; i--) {
newString += str[i]; // or newString = newString + str[i];
}
/* Here hello's length equals 5
For each iteration: i = str.length - 1 and newString = newString + str[i]
First iteration: i = 5 - 1 = 4, newString = "" + "o" = "o"
Second iteration: i = 4 - 1 = 3, newString = "o" + "l" = "ol"
Third iteration: i = 3 - 1 = 2, newString = "ol" + "l" = "oll"
Fourth iteration: i = 2 - 1 = 1, newString = "oll" + "e" = "olle"
Fifth iteration: i = 1 - 1 = 0, newString = "olle" + "h" = "olleh"
End of the FOR Loop*/

// Step 3. Return the reversed string
return newString; // "olleh"
}

reverseString('hello');

--> Reverse a String With Recursion
function reverseString(str) {
return (str === '' " ) ? " '' : reverseString(str.substr(1)) + str.charAt(0);
/*
First Part of the recursion method
You need to remember that you won’t have just one call, you’ll have several nested calls

Each call: str === "?" reverseString(str.subst(1)) + str.charAt(0)
1st call – reverseString("Hello") will return reverseString("ello") + "h"
2nd call – reverseString("ello") will return reverseString("llo") + "e"
3rd call – reverseString("llo") will return reverseString("lo") + "l"
4th call – reverseString("lo") will return reverseString("o") + "l"
5th call – reverseString("o") will return reverseString("") + "o"

Second part of the recursion method
The method hits the if condition and the most highly nested call returns immediately

5th call will return reverseString("") + "o" = "o"
4th call will return reverseString("o") + "l" = "o" + "l"
3rd call will return reverseString("lo") + "l" = "o" + "l" + "l"
2nd call will return reverserString("llo") + "e" = "o" + "l" + "l" + "e"
1st call will return reverserString("ello") + "h" = "o" + "l" + "l" + "e" + "h"
*/
}
reverseString("hello");

--> Check Palindrome using built-in Functions
function reverseString(str) {
var checkPalindrome = str.split("").reverse().join("");
if(checkPalindrome === str){
console.log("it is a plaindrome")
return checkPalindrome ;
}
else{
console.log("it is not plaindrome")
return str ;
}
}
var a = reverseString(prompt('Enter a string: '));
console.log(a)

--> Check Palindrome Using for Loop
1st method : reverse a string then match if both old and new string matches or not
function reverseString(str) {

var newString = "";

for(var i = str.length-1 ; i>=0 ; i--){
newString += str[i]
}

var b = newString === str ? (newString + " is a plaindrome") : (newString + " is not plaindrome");
return b;

}
var a = reverseString("madam");
console.log(a)

2nd method - check and match inside for loop if first letter matches last letter ot not
function checkPalindrome(str) {

// find the length of a string
const len = string.length;

// loop through half of the string
for (let i = 0; i < len / 2; i++) {

// check if first and last string are same
if (string[i] !== string[len - 1 - i]) {
return 'It is not a palindrome';
}
}
return 'It is a palindrome';
}

// take input
const string = prompt('Enter a string: ');

// call the function
const value = checkPalindrome(string);

console.log(value);

--> find number of matching characters

var b = (("hello, i am learning javascript".match(new RegExp("a", "g")) || []).length);
console.log(b)

--> Count the Number of Vowels Using Regex
function noOfVowels(str){
const count = str.match(/[aeiou]/gi).length;
return count;
}
var a = noOfVowels("Hello World");
console.log(a);

-->Count the Number of Vowels Using for Loop
function noOfVowels(str){
let count = "";
for (let letter of str.toLowerCase()){
if(vowels.includes(letter)){
count++;
}
}
return count;
}
var vowels = ["a","e","i","o","u"]
var a = noOfVowels("NO of vowels");
console.log(a);

--> calculate the number of vowels and consonants in a string in javascript
function noOfVowels(str){
let count = "";
let consonants = "";

for (let letter of str.toLowerCase()){
if(vowels.includes(letter)){
count++;

}
else{
consonants ++
}
}
console.log(count,"count");
console.log(consonants,"consonants");
return count;

}

var vowels = ["a","e","i","o","u"]
var a = noOfVowels("NO of vowels");
console.log(a);

--> How do you prove that the two strings are anagrams?
function checkAnagrams(a, b){
let lengthofa = a.length;
let lengthofb = b.length;

if(lengthofa !== lengthofb){
console.log("invalid")
}

var checka = a.split("").sort().join("");
var checkb = b.split("").sort().join("");

if(checka ===checkb){
return true
}
else{
return false
}
}

let a = checkAnagrams('hola','aloh')
console.log(a,'a')

--> Check Occurrence of a Character Using for Loop
function countString(str, letter) {
let count = 0;

// looping through the items
for (let i = 0; i < str.length; i++) {

// check if the character is at that position
if (str.charAt(i) == letter) {
count += 1;
}
}
return count;
}

// take input from the user
const string = prompt('Enter a string: ');
const letterToCheck = prompt('Enter a letter to check: ');

//passing parameters and calling the function
const result = countString(string, letterToCheck);

// displaying the result
console.log(result);

--> Check occurrence of a character using a Regex
function findChar (str,letter){
var re = new RegExp(letter,'g');
var count = str.match(re).length;
return count;
}
const stringToCheck = "Hello world";
const letterToCount = "l";
let result = findChar(stringToCheck, letterToCount)
console.log(result,'result')

--> How to verify if a number is prime or not in javascript