I'm studying node.js and have some interesting task - Write a program that finds and prints the biggest prime number which is <= N.
Input // Output - 13 // 13
126 // 113
26 // 23
In last course with java i have the same task and my code is really simple:
import java.util.Scanner;
public class BiggestPrimeNumber {
public static void main(String[] args){
int n;
Scanner in = new Scanner(System.in);
n=in.nextInt();
while(prim(n) == false){
n--;
}
System.out.println(n);
}
public static boolean prim(int m){
int n=m;
for(int i=2;i<n;i++){
if(n%i == 0){
return false;
}
}
return true;
}
}
I try similar way to test it, but I'm don't have idea how to convert it:
let n = 126;
while (isPrime(n) === false) {
n -= 1;
}
console.log(n);
let n = m;
for (let i = 2; i < n; i += 1) {
if (n % i === 0) {
return false;
}
}
return true;
Can you help me, because I'm really have problem with js using in console.
I think this is what you want. You only need to declare a function and use it as you are doing.
let n = 126;
while (isPrime(n) === false) {
n -= 1;
}
console.log(n);
function isPrime(m) {
let n = m;
for (let i = 2; i < n; i += 1) {
if (n % i === 0) {
return false;
}
}
return true;
}
If your running it with NodeJS in console, you can save it in a file called prime.js (for example) and execute it with: node prime.js.
You can pass parameters to the script like: node prime.js 126 and then get them in the code. That will be something like that:
const args = process.argv;
let n = args[2];
while (isPrime(n) === false) {
n -= 1;
}
console.log(n);
function isPrime(m) {
let n = m;
for (let i = 2; i < n; i += 1) {
if (n % i === 0) {
return false;
}
}
return true;
}
You're pretty close. First off, you don't have isPrime defined. Second, if you were to paste all of your code into the browser console, it isn't going to like that you are defining n twice. I also cleaned up your isPrime bit of code.
let n = 100;
let result = n;
const isPrime = num => {
for(let i = 2; i < num; i++)
if(num % i === 0) return false;
return num !== 1 && num !== 0;
}
while (isPrime(result) === false) {
result -= 1;
}
console.log(result + " is the next prime below " + n);
Also, remember that javascript is not a compiled language, so unless you are defining your function in a class, the browser will interpret the code sequentially. Therefore, you have to have isPrime defined before you use it.
The algorithm to find the nearest prime number can be further optimized. All prime numbers are of the form 6k+1 or 6k-1 except the numbers 2 and 3. Also, instead of checking all the way to the number the check can be made till Sqrt(n). Here is the modified isPrime function:
let n = 126;
while (isPrime(n) === false) {
n -= 1;
}
console.log(n);
function isPrime(num) {
if (num <= 1) return false;
if (num < 4) return true;
if (num%2 === 0 || num%3 === 0) return false;
for (var i = 5; i*i <= num; i+=6) {
if (num % i === 0 || num % (i + 2) === 0)
return false;
}
return true;
}
Related
I am trying to insert dashes ('-') between each two odd numbers and insert asterisks ('*') between each two even numbers, but I am only getting the last result.
I want to print out all the elements in the array.
For example: if num is 4546793 the output should be 454*67-9-3. I Did not count zero as an odd or even number.
function StringChallenge(num) {
let result = "";
for (let i = 0; i < num.length; i++) {
if (num[i] === 0) {
continue;
}
if (num[i - 1] % 2 == 0 && num[i] % 2 == 0) {
result = num[i - 1] + "*" + num[i];
continue;
}
if (num[i - 1] % 2 == !0 && num[i] % 2 == !0) {
result = num[i - 1] + "-" + num[i];
continue;
}
}
return result;
}
console.log(StringChallenge([4,5,4,6,7,9,3]));
You do not need to check as if&continue. Inserting given numbers to the result string and only adding "-" when index and previous are odd, and "*" when index and previous are even.
function StringChallenge(num) {
let result = "";
for (let i = 0; i < num.length; i++) {
if (num[i]%2 ===0) {// even
if(i !== 0 && num[i-1]%2===0){// previous is even either
result+="*"+num[i];
}else{
result+=num[i];
}
}else{// odd
if(i !== 0 && num[i-1]%2===1){// previous is odd either
result+="-"+num[i];
}else{
result+=num[i];
}
}
}
return result;
}
console.log(StringChallenge([4,5,4,6,7,9,3]));
Try this :)
function test(a){
let result=""
for(let i=0; i < a.length; i++){
if(a[i] != 0 && a[i-1] % 2 == 0 && a[i] % 2 == 0){
result = result + '*' + a[i]
}
else if (a[i] != 0 && a[i-1] % 2 != 0 && a[i] % 2 != 0){
result = result + '-' + a[i]
}
else{
result = result + a[i]
}
}
return result
}
console.log(test([4,5,4,6,7,9,3]));
As everyone has identified, the problem is you are not adding to result.
But here is a suggestion to make your code easier to read
// These one line functions make your code easier to read
function IsEven(num){
return num % 2 === 0;
}
function IsOdd(num){
return num % 2 !== 0;
}
function StringChallenge(numArray) {
// return empty string if not an array or empty array
if(!Array.isArray(numArray) || numArray.length === 0) return "";
let result = "" + numArray[0]; // use "" to coerce first element of numArray from number to string
for (let i = 1; i < numArray.length; i++) {
// focus on the conditions to determine the separator you want between each element
separator = "";
if (numArray[i] !== 0) {
if (IsEven(numArray[i]) && IsEven(numArray[i - 1])) {
separator = "*";
} else if (IsOdd(numArray[i]) && IsOdd(numArray[i - 1])){
separator = "-";
}
}
// build the result
result += separator + numArray[i];
}
return result;
}
I will do that this way :
== some advices for 2 cents ==
1 - try to make your code as readable as possible.
2 - use boolean tests rather than calculations to simply do a parity test
3 - ES7 has greatly improved the writing of JS code, so take advantage of it
console.log(StringChallenge([4,5,4,6,7,9,3])); // 454*67-9-3
function StringChallenge( Nums = [] )
{
const
isOdd = x => !!(x & 1) // Boolean test on binary value
, isEven = x => !(x & 1) && x!==0 // zero is not accepted as Even value
;
let result = `${Nums[0]??''}`; // get first number as
// result if Nums.length > 0
for (let i=1; i<Nums.length; i++)
{
if ( isOdd(Nums[i-1]) && isOdd(Nums[i]) ) result += '-';
if ( isEven(Nums[i-1]) && isEven(Nums[i]) ) result += '*';
result += `${Nums[i]}`; // same as Nums[i].toString(10);
}
return result
}
I hope this helps. I tried to keep it as simple as possible.
function StringChallenge(num) {
//start with a string to concatenate, or else interpreter tries to do math
operations
let result = num[0].toString();
function checkOdd(num){ //helper function to check if odd
return num % 2
}
for (let i = 0; i < num.length - 1; i++) {
if (checkOdd(num[i]) && checkOdd(num[i+1])) { //checks if both odd
result += `-${num[i+1]}`; //adds - and next number
} else if (!checkOdd(num[i]) && !checkOdd(num[i+1])) { //checks if both even
result += `*${num[i+1]}`; //adds * and next number
} else { //otherwise
result += num[i+1]; //just add next number
}
}
return result;
}
console.log(StringChallenge([4,5,4,6,7,9,3]));
Use +=. And, change your logic, your code prints out "4*67-99-3".
The zero check was pretty hard for me I hope the variables in my code explain itself. If not, let me know.
function even(num) {
return num % 2 === 0;
}
function odd(num) {
return num % 2 !== 0;
}
function StringChallenge(num) {
let result = "";
for (let i = 0; i < num.length; i++) {
var currentZero = num[i] === 0
var previousZero = num[i-1] === 0
var bothEven = even(num[i]) && even(num[i-1])
var bothOdd = odd(num[i]) && odd(num[i-1])
var firstNumber = (i === 0)
if (!currentZero) {
if (firstNumber) {
result += num[i]
} else {
if (bothEven && !previousZero) {
result += "*" + num[i]
} else if (bothOdd && !currentZero) {
result += "-" + num[i]
} else {
result += num[i]
}
}
}
}
return result;
}
console.log(StringChallenge([0,4,5,0,4,6,7,9,3]));
When I try to run the input, it says that the time limit exceeded. Can anyone help me to reduce this code, thank you.
const counterGame = (n) => {
let count = 0;
for (let i = n; i > 0; i--) {
if (Math.pow(2, i) % 1 === 0 && Math.pow(2, i) === n) {
n /= 2;
count++;
if (n === 1) break;
} else if (Math.pow(2, i) <= n) {
n -= Math.pow(2, I);
count++;
if (n === 1) break;
}
}
if (count % 2 === 0) {
return 'Richard';
} else {
return 'Louise';
}
};
You don't have to iterate over the values to find if n is power of 2. You can use Math.log2() method. Like this,
function counterGame(n) {
let move = 0;
while(n > 1) {
let power = parseInt(Math.log2(n));
let max = 2**power;
if(n === max) {
n = parseInt(n/2);
} else {
n = n - max;
}
move++;
}
if(move %2 === 0) {
return 'Richard';
} else {
return 'Louise';
}
}
console.log(counterGame(6));
console.log(counterGame(8));
You don't need to loop for just checking whether n is power of 2. Check whether this helps or not.
const counterGame = (n) => {
if (n % 2 === 0) {
return 'Richard';
} else {
return 'Louise';
}
};
Question
A prime number is a whole number greater than 1 with exactly two divisors: 1 and itself. For example, 2 is a prime number because it is only divisible by 1 and 2. In contrast, 4 is not prime since it is divisible by 1, 2 and 4.
Rewrite sumPrimes so it returns the sum of all prime numbers that are less than or equal to num.
My Attempt
const isPrime = a => {
for(let i = 2; i < a; i++)
if(num % i === 0) return false;
return a > 1;
}
function sumPrimes(num, total = []) {
let numVar = num;
let n = total.reduce((aggregate, item)=>{
return aggregate + item;
}, 0);
if(n > numVar){
return n;
}
for(let i = 1; i <= numVar; i++){
if(isPrime(i)== true){
total.push(i);
}
}
return sumPrimes(num, total);
}
sumPrimes(10);
The Problem
It says: 'Num is not defined'
I am not sure if there are other errors.
My Question
Please could you help me find the error, and fix the code to solve the algorithm?
This was a simple syntax error identified by #Jonas Wilms (upvote him in the comment above :))!
By replacing the 'a' with 'num' the function was fixed.
const isPrime = a => {
for(let i = 2; i < a; i++)
if(a % i === 0) return false;
return a > 1;
}
function sumPrimes(num, total = []) {
let numVar = num;
let n = total.reduce((aggregate, item)=>{
return aggregate + item;
}, 0);
if(n > numVar){
return n;
}
for(let i = 1; i <= numVar; i++){
if(isPrime(i)== true){
total.push(i);
}
}
return sumPrimes(num, total);
}
console.log(sumPrimes(10));
this simple function may help you,
function isPrime(num) {
for (var i = 2; i < num; i++)
if (num % i === 0) return false;
return num > 1;
}
function sumPrimes(num) {
let tot = 0;
for (let i = 0; i < num; i++)
if (isPrime(i))
tot += i;
return tot;
}
console.log(sumPrimes(10));
var number = prompt('Input a number!');
var n = number;
function getList() {
for (var n = 1; n <= 17; n++) {
if (n % 3 == 0 || n % 5 == 0)
console.log (n);
}
}
console.log(getList());
console.log((n*(n+1))/2);
//equation for summation: (n*(n+1))/2
I'm trying to return the sum of numbers divisible by 3 or 5 up to 17. So far, it half-works; it lists all the numbers, but I can't find a way to return the sum.
I have the equation for summation, but I can't find a way to put it in so that it works. How do you get the equation to reference the list instead of referencing the inputted number?
The answer is supposed to be 60. Any clue? Thanks!
var sum = 0;
for (var n = 1; n <= 17; n++) {
if (n % 3 === 0 || n % 5 === 0)
sum += n;
}
console.log(sum);
Use a variable to add the numbers and return it after for loop.
Below it the exapmle.
function getList() {
var sum = 0;
for (var n = 1; n <= 17; n++) {
if (n % 3 == 0 || n % 5 == 0) {
sum += n;
}
}
return sum;
}
console.log(getList());
Two things:
Just return the sum from your getList function
Make sure your prompt input is converted to integer otherwise it will be treated as a string and your n*(n+1)/2 will be wrong
var number = parseInt(prompt('Input a number!'));
var n = number;
function getList() {
var sum = 0;
for (var n = 1; n <= 17; n++) {
if (n % 3 == 0 || n % 5 == 0) {
console.log (n);
sum += n;
}
}
return sum;
}
console.log(getList());
console.log(n, (n*(n+1))/2);
If you want an equation :)
function sumOfNumbersDivisibleBy3Or5(n) {
const by3 = Math.floor(n/3),
by5 = Math.floor(n/5),
by3And5 = Math.floor(n/3/5);
return 3*by3*(by3+1)/2 + 5*by5*(by5 + 1)/2 - 3*5*by3And5*(by3And5 + 1)/2
}
console.log(sumOfNumbersDivisibleBy3Or5(17))
var number = prompt('Input a number!');
function getList() {
var sum = 0;
for (var n = 1; n <= number; n++) {
if (n % 3 == 0 || n % 5 == 0)
sum+=n;
}
return sum;
}
console.log(getList());
it will return sum of all the number which is divisible by 3 or 5 in between 1 and entered number
What have I done wrong with this code? It can't print anything on the console.
Here it is the description of the problem:
Implement a javascript function that accepts an array containing an integer N and uses an expression to check if given N is prime (i.e. it is divisible without remainder only to itself and 1).
var n = ['2'];
function isPrime(n) {
if (n < 2) {
return false;
}
var isPrime = true;
for(var i = 2; i < Math.sqrt(n); i += 1) {
if (n % i === 0) {
isPrime = false;
}
}
return isPrime;
}
return isPrime(n);
There are couple errors in your code.
First, you need to check for every integer between 2 and Math.sqrt(n) inclusively. Your current code returns true for 4.
I don't think this is in a function, so you need to omit return from return isPrime(n) and replace it with a function wich prints out the return value of the funnction, like alert or console.log.
n is not a number, it's an array. You need to either make n a number, or call the function with isPrime(n[0]).
The correct code is
var n = 2;
function isPrime(n) {
if (n < 2) {
return false;
}
var isPrime = true;
for(var i = 2; i <= Math.sqrt(n); i += 1) {
if (n % i === 0) {
isPrime = false;
}
}
return isPrime;
}
alert(isPrime(n));
Note: You can change n += 1 to n++, and it works the same way.
n is an array, you want to access first element in the array and convert it to number first.
try replacing
return isPrime(n);
with
return isPrime(parseInt(n[0],10));
Your for-loop condition also needs a little modification
for(var i = 2; i <= Math.sqrt(n); i += 1) { //observe that i is not <= Math.sqrt(n)
A couple of little errors:
var n = 2;//<--no need to put n in an array
function isPrime(n) {
if (n < 2) {
return false;
}
var isPrime = true;
for(var i = 2; i < Math.sqrt(n); i += 1) {
if (n % i === 0) {
isPrime = false;
}
}
return isPrime;
}
isPrime(n);//<--no need for "return"
As to no output being printed, it is because you need to use console.log.
Replace return isPrime(n); with console.log(isPrime(n));.
Full working code:
var n = ['2', '3', '4', '5', '6', '7']; // you can use as many values as you want
function isPrime(n) {
if (n < 2) {
return false;
}
var isPrime = true;
for (var i = 2; i <= Math.sqrt(n); i += 1) { // Thanks to gurvinder372's comment
if (n % i === 0) {
isPrime = false;
}
}
return isPrime;
}
n.forEach(function(value) { // this is so you can iterate your array with js
console.log('is ' + value + ' prime or not? ' + isPrime(value)); // this so you can print a message in the console
});
/*
// Another approach of parsing the data, uncomment this piece of code and comment the one above to see it in action (both will give the same result)
for (index = 0; index < n.length; ++index) {
console.log('is ' + n[index] + ' prime or not? ' + isPrime(n[index])); // this so you can print a message in the console
}
*/