I was trying to write a program that returns the largest palindromic number, which is the product of two simple five-digit numbers, and returns the factors themselves.
A prime number is a natural number that is divided only by 1 and itself (2, 3, 5, 7, 11, ...)
A palindromic number reads the same both ways (for example, ABBA).
if(isPalin(mul) && isPrime(i) && isPrime(j))
function isPrime(i){
for (var k = 2; k <= i; k++) {
if (i%k===0 && i!==k) {
return false;
}
}
return true;
}
<!--code-->
<script>
function largestPalindrome(){
for(var i = 99999; i>10000; i--){
for(var j = 99999; j>10000; j--){
var mul = j*i;
if(isPalin(mul) && isPrime(i) && isPrime(j)){
return i * j;
}
}
}
}
function isPalin(i){
return i.toString() == i.toString().split("").reverse().join("");
}
function isPrime(i){
for (var k = 2; k <= i; k++) {
if (i%k===0 && i!==k) {
return false;
}
}
return true;
}
console.log(largestPalindrome());
</script>
When I run this program it does not display anything in the console and I am not sure why.
Look this link for time-complexity of algorithms. Also this to see how time-complexity can influence to your program efficiency.
This part is not very precise but it can help. Your first loop runs 99999-10000 time. Also this holds for second loop. The isPrime in the worst case runs (99999). So if (i%k===0 && i!==k) return false; runs total_ops = (99999-10000)^2*(99999) times(we skip other part of your code). If your program written in c++ which is more faster than java-script it can run about 2*(10^8) simple operation per second. Your program run time is about(obviously more than) total_ops/(2*10^8) (I suggest calculate it to have an estimation...).
PS: You can put print to your functions to ensure about their progress...
Problem:: Time Complexity
improvements
isPrime()
function isPrime(n)
{
// Corner cases
if (n <= 1) return false;
if (n <= 3) return true;
// This is checked so that we can skip
// middle five numbers in below loop
if (n%2 == 0 || n%3 == 0) return false;
for (var i=5; i*i<=n; i=i+6)
if (n%i == 0 || n%(i+2) == 0)
return false;
return true;
}
you isprime function is not optimized one. You should use this.
Don't find every prime number 2 times.! Just find all prime numbers once, store them into a list, and then pick every number from prime list and check if it is palindrome.
var primelist = [];
for(var i = 99999; i > 10000; i++)
{
if(isprime(i))
{
primelist.push(i);
}
}
for (var i = 0; i < primelist.length; i++) {
for (var j = 0; j < primelist.length; j++)
{
if(isPalindrome(i*j))
{
// Number you want.
return (i*j);
}
}
}
to check , start from the largest prime numbers.
a 5 digit number starts from 10000 to 99999 instead of 11111 to 99999. Although, It does not change the output of the function.
I'm trying to solve this exercise. There is a string of numbers and among the given numbers the program finds one that is different in evenness, and returns a position of this number. The element has to be returned by its index (with the number being the actual position the number is in). If its index 0, it has to be returned as 1. I have this so far but it's not passing one test. I'm not too sure why because it feels like it should. Is anyone able to see what the error is? Any help is appreciated!
function iqTest(numbers) {
var num = numbers.split(" ");
var odd = 0;
var even = 0;
var position = 0;
for(var i = 0; i < num.length; i++) {
if(num[i]%2!==0) {
odd++;
if(odd===1) {
position = num.indexOf(num[i]) + 1;
}
}
else if(num[i]%2===0) {
even++;
if(even===1) {
position = num.indexOf(num[i]) + 1;
}
}
}
return position;
}
iqTest("2 4 7 8 10") output 3
iqTest("2 1 2 2") output 2
iqTest("1 2 2") outputs 2 when it should be 1
The simplest way is to collect all even/odd positions in subarrays and check what array has the length 1 at the end:
function iqTest(numbers) {
numbers = numbers.split(' ');
var positions = [[], []];
for (var i = 0; i < numbers.length; i++) {
positions[numbers[i] % 2].push(i + 1);
}
if(positions[0].length === 1) return positions[0][0];
if(positions[1].length === 1) return positions[1][0];
return 0;
}
console.log(iqTest("2 4 7 8 10"))
console.log(iqTest("2 1 2 2"))
console.log(iqTest("1 2 2"))
console.log(iqTest("1 3 2 2"))
Your code is overly complex.
Since the first number determines whether you're looking for an even number or an odd one, calculate it separately. Then, find the first number that doesn't match it.
function iqTest(numbers) {
numbers = numbers.split(" ");
var parity = numbers.shift() % 2;
for( var i=0; i<numbers.length; i++) {
if( numbers[i] % 2 != parity) {
return i+2; // 1-based, but we've also skipped the first
}
}
return 0; // no number broke the pattern
}
That being said, iqTest("1 2 2") should return 2 because the number in position 2 (the first 2 in the string) is indeed the first number that breaks the parity pattern (which 1 has established to be odd)
You have to define which "evenness" is the different one. Use different counters for the two cases, and return -1 if you don't have a single different one. Something like this:
function iqTest(numbers) {
var num = numbers.split(" ");
var odd = 0;
var even = 0;
var positionOdd = 0;
var positionEven = 0;
for(var i = 0; i < num.length; i++) {
if(num[i]%2!==0) {
odd++;
if(odd===1) {
positionOdd = i + 1;
}
}
else if(num[i]%2===0) {
even++;
if(even===1) {
positionEven = i + 1;
}
}
}
if (odd == 1)
return positionOdd;
else if (even == 1)
return positionEven;
else
return -1;
}
Note that, if you have exactly a single even number and a single odd one, the latter will be returned with the method of mine. Adjust the logic as your will starting from my solution.
Since the first number determines whether you're looking for an even number or an odd one, calculate it separately.
Then, find the first number that doesn't match it.
function iqTest(numbers){
// ...
const numArr = numbers.split(' ');
const checkStatus = num => (parseInt(num) % 2) ? 'odd' : 'even';
const findUniqueStatus = array => {
let numEvens = 0;
array.forEach(function(value){
if (checkStatus(value) == 'even') { numEvens++; }
});
return (numEvens === 1) ? 'even' : 'odd'
}
let statuses = numArr.map(checkStatus),
uniqueStatus = findUniqueStatus(numArr);
return statuses.indexOf(uniqueStatus) + 1;
}
}
public static int Test(string numbers)
{
var ints = numbers.Split(' ');
var data = ints.Select(int.Parse).ToList();
var unique = data.GroupBy(n => n % 2).OrderBy(c =>
c.Count()).First().First();
return data.FindIndex(c => c == unique) + 1;
}
The answer I'm getting is not the correct one (correct answer is 906609). Please help me understand where I am going wrong. I want the while loop to go from 100 to 999 while multiplying itself against the current i value before the loop increments it.
// A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
// Find the largest palindrome made from the product of two 3-digit numbers.
var pali = [];
function palindrome() {
for (var i = 100; i <= 999; i++) {
var counter = 100;
while (counter <= 999) {
var result = counter * i;
if (result.toString() === result.toString().split("").reverse().join("")) {
pali.push(result);
}
counter++;
}
}
return pali[pali.length - 1];
}
console.log(palindrome());
You're going to have to sort the array in ascending order if you want the last one to be the highest:
pali.sort(function(a, b){return a-b});
Using that, I get 906609.
Lengthier, but faster. Starting at the max values and working down, short circuiting when we won't find higher values:
function largestPalindromeProduct(lower, upper) {
var palindrome = 0;
var outerLow = lower;
var outer = upper;
while (outer > outerLow) {
var inner = upper;
var innerLow = lower;
while (inner > innerLow) {
var result = inner * outer;
if (result + "" === (result + "").split("").reverse().join("")) {
if (result > palindrome) {
palindrome = result;
outerLow = inner; // Don't go lower than this value in the outer, no need!
}
inner = innerLow; // short-circuit this loop
}
inner--;
}
outer--;
}
return palindrome;
}
console.log(largestPalindromeProduct(100, 999))
I think the easiest way will be to add a If statement.
function palindrome()
{
var max = 0;
for (var i = 999; i >= 100; i--)
{
var counter = 999;
while (counter >= 100)
{
var result = counter * i;
if (result.toString() === result.toString().split("").reverse().join(""))
{
if(result>max)
{
max = result;
}
}
counter++;
}
}
return max;
}
I am new to Javascript, I am doing a coding challenge to learn more about the language. This is not school related or anything like that, totally for my own personal growth. Here is the challenge:
Return the sum of all odd Fibonacci numbers up to and including the
passed number if it is a Fibonacci number.
I have spent the past 2 evenings working on solving this challenge. When I run my code using underscore.js it works. When I use Ramda.js it says NaN. I would think both would return NaN. I'm very surprised that I can get the correct answer from one and not the other. Any insights would be greatly appreciated!
var R = require('ramda');
function sumFibs(num) {
var fib_Arr = [];
var new_Arr = [];
var total = 0;
// I use this to tell if the fib num is greater than 2
var the_Bit = "false";
// This is used to keep track of when to stop the loop
var fib_Num = 0;
// THIS WORKS FROM HERE
// This loop generates a list of fibonacci numbers then pushes them to the fib_Arr
for(var i = 0; total < num; i++){
if (i < 1){
fib_Arr.push(0);
}
else if (i === 1){
fib_Arr.push(i);
fib_Arr.push(1);
}
else if (i === 2){
fib_Arr.push(2);
the_Bit = "true";
}
else if (the_Bit === "true"){
temp_Arr = R.last(fib_Arr,2);
temp_Arr = temp_Arr[0] + temp_Arr[1];
fib_Arr.push(temp_Arr);
total = R.last(fib_Arr);
}
// Generating the fib Array works TO HERE!!!!
}
// console.log(fib_Arr); // Print out the generated fibonacci array
// if last Array element is greater than the original in
var last_Element = R.last(fib_Arr);
if (last_Element > num){
console.log("The last element of the array is bigger!");
fib_Arr.splice(-1,1); // This removes the last item from the array if it is larger than the original num input
}
// This loop removes all of the EVEN fibonacci numbers and leaves all of the ODD numbers
for (var j = 0; j < fib_Arr.length; j++){
if (fib_Arr[j] % 2 !== 0){
new_Arr.push((fib_Arr[j]));
}
}
// This checks if the original input num was a
if (num % 2 !== 0){
new_Arr.push(num);
}
else{
console.log("The original num was not a Fibonacci number!");
}
// if last Array element is the same as the original input num
var last = R.last(fib_Arr);
if (last === num){
console.log("Removing the last element of the array!");
new_Arr.splice(-1,1); // This removes the last item from the array if it is the same as the original num input
}
// Now to add all of the numbers up :-)
for (var k = 0; k < new_Arr.length; k++){
console.log("This is fib_Num: " + fib_Num);
// console.log(fib_N`);
fib_Num = fib_Num += new_Arr[k];
}
return fib_Num;
}
// TEST CASES:
// console.log(sumFibs(75025)); //.to.equal(135721);
console.log(sumFibs(75024)); //.to.equal(60696);
You have a problem on these lines :
temp_Arr = R.last(fib_Arr,2);
temp_Arr = temp_Arr[0] + temp_Arr[1];
Besides the fact that R.last does not take a second argument (that will not fail though), you are using temp_arr as an array, when it is a number. Therefore, temp_arr gets a NaN value.
You are probably looking for R.take (combined with R.reverse) or R.slice.
By changing :
temp_Arr = R.last(fib_Arr,2);
with :
temp_Arr = R.take(2, R.reverse(fib_Arr));
or with :
temp_Arr = R.slice(fib_Arr.length - 2, fib_Arr.length)(fib_Arr);
or with (bonus play with a reduce from the right) :
temp_Arr = R.reduceRight(function(arr, elem) {
return arr.length < 2 ? [elem].concat(arr) : arr;
}, [])(fib_Arr);
We get :
sumFibs(75024) === 60696
For the record, here's how you do this problem:
function fibSumTo(n) {
var f1 = 1, f2 = 1, sum = 1, t;
while (f2 <= n) {
if (f2 & 1) sum += f2;
t = f1 + f2;
f1 = f2;
f2 = t;
}
return sum;
}
There's really no need for any sort of library because there's really no need for any sort of data structure.
var _ = require('underscore');function sumUpFibs (number){
arr_of_fibs = [1,1];
current = 1; //cursor for previous location
while (true){
var num = arr_of_fibs[current] + arr_of_fibs[current - 1];
if (num <= number) {
arr_of_fibs.push(num);
current++;
} else {
break;
}
}
console.log(arr_of_fibs);
var total = 0;
_.each(arr_of_fibs, function(fib){
total += fib;
})
return total;}console.log(sumUpFibs(75025));
This may be a better implementation... Though I know you're just starting so I don't want to come off as mean : D.... Also, maybe check your test cases too.
I am just starting JS, and understand the concept of finding a factor. However, this snippet of code is what I have so far. I have the str variable that outputs nothing but the first factor which is 2. I am trying to add each (int) to the str as a list of factors. What's the wrong in below code snippet?
function calculate(num) {
var str = "";
var int = 2;
if (num % int == 0) {
str = str + int;
int++;
} else {
int++;
}
alert(str);
}
calculate(232);
UPDATED ES6 version:
As #gengns suggested in the comments a simpler way to generate the array would be to use the spread operator and the keys method:
const factors = number => [...Array(number + 1).keys()].filter(i=>number % i === 0);
console.log(factors(36)); // [1, 2, 3, 4, 6, 9, 12, 18, 36]
ES6 version:
const factors = number => Array
.from(Array(number + 1), (_, i) => i)
.filter(i => number % i === 0)
console.log(factors(36)); // [1, 2, 3, 4, 6, 9, 12, 18, 36]
https://jsfiddle.net/1bkpq17b/
Array(number) creates an empty array of [number] places
Array.from(arr, (_, i) => i) populates the empty array with values according to position [0,1,2,3,4,5,6,7,8,9]
.filter(i => ...) filters the populated [0,1,2,3,4,5] array to the elements which satisfy the condition of number % i === 0 which leaves only the numbers that are the factors of the original number.
Note that you can go just until Math.floor(number/2) for efficiency purposes if you deal with big numbers (or small).
As an even more performant complement to #the-quodesmith's answer, once you have a factor, you know immediately what its pairing product is:
function getFactors(num) {
const isEven = num % 2 === 0;
const max = Math.sqrt(num);
const inc = isEven ? 1 : 2;
let factors = [1, num];
for (let curFactor = isEven ? 2 : 3; curFactor <= max; curFactor += inc) {
if (num % curFactor !== 0) continue;
factors.push(curFactor);
let compliment = num / curFactor;
if (compliment !== curFactor) factors.push(compliment);
}
return factors;
}
for getFactors(300) this will run the loop only 15 times, as opposed to +-150 for the original.
#Moob's answer is correct. You must use a loop. However, you can speed up the process by determining if each number is even or odd. Odd numbers don't need to be checked against every number like evens do. Odd numbers can be checked against every-other number. Also, we don't need to check past half the given number as nothing above half will work. Excluding 0 and starting with 1:
function calculate(num) {
var half = Math.floor(num / 2), // Ensures a whole number <= num.
str = '1', // 1 will be a part of every solution.
i, j;
// Determine our increment value for the loop and starting point.
num % 2 === 0 ? (i = 2, j = 1) : (i = 3, j = 2);
for (i; i <= half; i += j) {
num % i === 0 ? str += ',' + i : false;
}
str += ',' + num; // Always include the original number.
console.log(str);
}
calculate(232);
http://jsfiddle.net/r8wh715t/
While I understand in your particular case (calculating 232) computation speed isn't a factor (<-- no pun intended), it could be an issue for larger numbers or multiple calculations. I was working on Project Euler problem #12 where I needed this type of function and computation speed was crucial.
function calculate(num) {
var str = "0";
for (var i = 1; i <= num; i++) {
if (num % i == 0) {
str += ',' + i;
}
}
alert(str);
}
calculate(232);
http://jsfiddle.net/67qmt/
Below is an implementation with the time complexity O(sqrt(N)):
function(A) {
var output = [];
for (var i=1; i <= Math.sqrt(A); i++) {
if (A % i === 0) {
output.push(i);
if (i !== Math.sqrt(A)) output.push(A/i);
}
}
if (output.indexOf(A) === -1) output.push(A);
return output;
}
here is a performance friendly version with complexity O(sqrt(N)).
Output is a sorted array without using sort.
var factors = (num) => {
let fac = [], i = 1, ind = 0;
while (i <= Math.floor(Math.sqrt(num))) {
//inserting new elements in the middle using splice
if (num%i === 0) {
fac.splice(ind,0,i);
if (i != num/i) {
fac.splice(-ind,0,num/i);
}
ind++;
}
i++;
}
//swapping first and last elements
let temp = fac[fac.length - 1];
fac[fac.length - 1] = fac[0];
fac[0] = temp;
// nice sorted array of factors
return fac;
};
console.log(factors(100));
Output:
[ 1, 2, 4, 5, 10, 20, 25, 50, 100 ]
This got me an 85% on Codility (Fails on the upperlimit, over a billion).
Reducing the input by half doesn't work well on large numbers as half is still a very large loop. So I used an object to keep track of the number and it's half value, meaning that we can reduce the loop to one quarter as we work from both ends simultaneously.
N=24 becomes: (1&24),(2&12),(3&8),(4&6)
function solution(N) {
const factors = {};
let num = 1;
let finished = false;
while(!finished)
{
if(factors[num] !== undefined)
{
finished = true;
}
else if(Number.isInteger(N/num))
{
factors[num] = 0;
factors[N/num]= 0;
}
num++
}
return Object.keys(factors).length;
}
Using generators in typescript in 2021
function* numberFactorGenerator(number: number): Generator<number> {
let i: number = 0;
while (i <= number) {
if (number % i === 0) {
yield i;
}
i++;
}
}
console.log([...numberFactorGenerator(12)]); // [ 1, 2, 3, 4, 6, 12 ]
function factorialize(num) {
var result = '';
if( num === 0){
return 1;
}else{
var myNum = [];
for(i = 1; i <= num; i++){
myNum.push(i);
result = myNum.reduce(function(pre,cur){
return pre * cur;
});
}
return result;
}
}
factorialize(9);
I came looking for an algorithm for this for use in factoring quadratic equations, meaning I need to consider both positive and negative numbers and factors. The below function does that and returns a list of factor pairs. Fiddle.
function getFactors(n) {
if (n === 0) {return "∞";} // Deal with 0
if (n % 1 !== 0) {return "The input must be an integer.";} // Deal with non-integers
// Check only up to the square root of the absolute value of n
// All factors above that will pair with factors below that
var absval_of_n = Math.abs(n),
sqrt_of_n = Math.sqrt(absval_of_n),
numbers_to_check = [];
for (var i=1; i <= sqrt_of_n; i++) {
numbers_to_check.push(i);
}
// Create an array of factor pairs
var factors = [];
for (var i=0; i <= numbers_to_check.length; i++) {
if (absval_of_n % i === 0) {
// Include both positive and negative factors
if (n>0) {
factors.push([i, absval_of_n/i]);
factors.push([-i, -absval_of_n/i]);
} else {
factors.push([-i, absval_of_n/i]);
factors.push([i, -absval_of_n/i]);
}
}
}
// Test for the console
console.log("FACTORS OF "+n+":\n"+
"There are "+factors.length+" factor pairs.");
for (var i=0; i<factors.length; i++) {
console.log(factors[i]);
}
return factors;
}
getFactors(-26);
function calculate(num){
var str = "0" // initializes a place holder for var str
for(i=2;i<num;i++){
var num2 = num%i;
if(num2 ==0){
str = str +i; // this line joins the factors to the var str
}
}
str1 = str.substr(1) //This removes the initial --var str = "0" at line 2
console.log(str1)
}
calculate(232);
//Output 2482958116
Here's an optimized solution using best practices, proper code style/readability, and returns the results in an ordered array.
function getFactors(num) {
const maxFactorNum = Math.floor(Math.sqrt(num));
const factorArr = [];
let count = 0; //count of factors found < maxFactorNum.
for (let i = 1; i <= maxFactorNum; i++) {
//inserting new elements in the middle using splice
if (num % i === 0) {
factorArr.splice(count, 0, i);
let otherFactor = num / i; //the other factor
if (i != otherFactor) {
//insert these factors in the front of the array
factorArr.splice(-count, 0, otherFactor);
}
count++;
}
}
//swapping first and last elements
let lastIndex = factorArr.length - 1;
let temp = factorArr[lastIndex];
factorArr[lastIndex] = factorArr[0];
factorArr[0] = temp;
return factorArr;
}
console.log(getFactors(100));
console.log(getFactors(240));
console.log(getFactors(600851475143)); //large number used in Project Euler.
I based my answer on the answer written by #Harman
We don't have to loop till end of the given number to find out all the factors. We just have to loop till reaching the given number's squareroot. After that point we, can figure out the rest of the factors by dividing the given number with the already found factors.
There is one special case with this logic. When the given number has a perfect square, then the middle factor is duplicated. The special case is also handled properly in the below code.
const findFactors = function (num) {
const startingFactors = []
const latterFactors = []
const sqrt = Math.sqrt(num)
for (let i = 1; i <= sqrt; i++) {
if (num % i == 0) {
startingFactors.push(i)
latterFactors.push(num / i)
}
}
// edge case (if number has perfect square, then the middle factor is replicated, so remove it)
if (sqrt % 1 == 0) startingFactors.pop()
return startingFactors.concat(latterFactors.reverse())
}
function factorialize(num) {
if(num === 0)
return 1;
var arr = [];
for(var i=1; i<= num; i++){
arr.push(i);
}
num = arr.reduce(function(preVal, curVal){
return preVal * curVal;
});
return num;
}
factorialize(5);