Develop Reference

Get all substrings of a string in JavaScript

I have the following function to get all of the substrings from a string in JavaScript. I know it's not correct but I feel like I am going about it the right way. Any advice would be great.
var theString = 'somerandomword',
allSubstrings = [];
getAllSubstrings(theString);
function getAllSubstrings(str) {
var start = 1;
for ( var i = 0; i < str.length; i++ ) {
allSubstrings.push( str.substring(start,i) );
}
}
console.log(allSubstrings)
Edit: Apologies if my question is unclear. By substring I mean all combinations of letters from the string (do not have to be actual words) So if the string was 'abc' you could have [a, ab, abc, b, ba, bac etc...] Thank you for all the responses.

You need two nested loop for the sub strings.
function getAllSubstrings(str) {
var i, j, result = [];
for (i = 0; i < str.length; i++) {
for (j = i + 1; j < str.length + 1; j++) {
result.push(str.slice(i, j));
}
}
return result;
}
var theString = 'somerandomword';
console.log(getAllSubstrings(theString));
.as-console-wrapper { max-height: 100% !important; top: 0; }

A modified version of Accepted Answer. In order to give the minimum string length for permutation
function getAllSubstrings(str, size) {
var i, j, result = [];
size = (size || 0);
for (i = 0; i < str.length; i++) {
for (j = str.length; j - i >= size; j--) {
result.push(str.slice(i, j));
}
}
return result;
}
var theString = 'somerandomword';
console.log(getAllSubstrings(theString, 6));

Below is a recursive solution to the problem
let result = [];
function subsetsOfString(str, curr = '', index = 0) {
if (index == str.length) {
result.push(curr);
return result;
}
subsetsOfString(str, curr, index + 1);
subsetsOfString(str, curr + str[index], index + 1);
}
subsetsOfString("somerandomword");
console.log(result);

An answer with the use of substring function.
function getAllSubstrings(str) {
var res = [];
for (let i = 0; i < str.length; i++) {
for (let j = i + 1; j <= str.length; j++) {
res.push(str.substring(i, j));
}
}
return res;
}
var word = "randomword";
console.log(getAllSubstrings(word));

function generateALlSubstrings(N,str){
for(let i=0; i<N; i++){
for(let j=i+1; j<=N; j++){
console.log(str.substring(i, j));
}
}
}

Below is a simple approach to find all substrings
var arr = "abcde";
for(let i=0; i < arr.length; i++){
for(let j=i; j < arr.length; j++){
let bag ="";
for(let k=i; k<j; k++){
bag = bag + arr[k]
}
console.log(bag)
}
}

function getSubstrings(s){
//if string passed is null or undefined or empty string
if(!s) return [];
let substrings = [];
for(let length = 1 ; length <= s.length; length++){
for(let i = 0 ; (i + length) <= s.length ; i++){
substrings.push(s.substr(i, length));
}
}
return substrings;
}

finding prime numbers in an array from 1-200

A math problem describes a list of numbers from 1-200, you must skip the number 1, and then for each number that follows, remove all multiples of that number from the list. Do this until you have reached the end of the list.
Here's what I have so far.
var x = []; // creating an array called x with zero numbers
for ( var i = 1; i <= 200; i++ ){
x.push(i);
};
// x now should have an array that contains the intergers from 1-200.
//looping through the array.
for ( var i = 0; i <= x.length; i++ ){ //going from 1-200
if (x[i] == 1){
continue; // skipping 1
} else {
for ( var n = i+1; n <= i; n++){ // take the number 1 index bigger than x[i]
if ( n % i == 0){ //find if the modulus of x[n] and x[i] is zeor, meaning it is divisible by x[i]
x.shift(); //remove that number
console.log(x[n]);
} else {
continue;
}
}
}
};

Instead of adding number 1 to 200 and then removing non prime numbers, try only putting prime numbers into that list. Since this is a school problem (I'm guessing) I don't want to give you the answer, but if you have more questions I can answer.
Also your nested loop will never run, go over that logic again.

Another version (a minute too late, as always ;-), one with comments
// lil' helper
function nextSet(a,n){
while(a[n] == 0) n++;
return n;
}
function setPrimes(a,n){
var k, j, r;
n = n + 1;
k = n;
while(k--)a[k] = 1;
a[0] = 0; // number 0
a[1] = 0; // number 1
// get rid of all even numbers
for(k = 4; k < n; k += 2) {
a[k] = 0;
}
// we don't need to check all of the numbers
// because sqrt(x)^2 = x
r = Math.floor(Math.sqrt(n));
k = 0;
while(k < n){
k = nextSet(a,k+1);
// a test if we had them all
if(k > r){
break;
}
// unmark all composites
for(j = k * k; j < n; j += 2*k){
a[j] = 0;
}
}
return a;
}
function getPrimes(n){
// we know the size of the input
var primearray = new Array(n);
// we don't know the size of the output
// prime-counting is still an unsolved problem
var output = [];
setPrimes(primearray, n);
for(var i = 0; i < n; i++){
if(primearray[i] == 1){
output.push(i);
}
}
return output;
}
getPrimes(200);
You can go through a full implementation of that algorithm at another primesieve.

Here is, I believe, a working example of what you want:
function isPrime(num){
if(num < 2){
return false;
}
for(var i=2,l=Math.sqrt(num); i<=l; i++){
if(num % i === 0){
return false;
}
}
return true;
}
function range(f, t){
for(var i=f,r=[]; i<=t; i++){
r.push(i);
}
return r;
}
function primeRange(from, to){
var a = range(from, to), r = [];
for(var i=0,l=a.length; i<l; i++){
var v = a[i];
if(isPrime(v)){
r.push(v);
}
}
return r;
}
var prmRng = primeRange(1, 200);
console.log(prmRng);

I solved it this way:
let numbers = new Array();
for (let i = 1; i <= 200; i++) {
numbers.push(i);
}
let primeNumbers = (num) => {
let prime = new Array();
for(let i = 0; i < num.length; i++) {
let count = 0;
for (let p = 2; p <= num[i]; p++) {
if(num[i] % p === 0 && num[i] !== 2) {
count++;
} else {
if(num[i] === 2 || count === 0 && num[i]-1 === p) {
prime[i] = num[i];
}
}
}
}
return prime.filter(Boolean);
}
console.log(primeNumbers(numbers));

Print prime numbers between 0 and 100

I'm trying to print all prime number between 0 and 100, but when executing this code the browser's tab just outputs nothing!!
for(var i = 2; i < 100; i++)
{
var prime = [];
for(var j = 0; j <= i; j++)
{
var p = i % j;
}
if(p != 0) prime.push(i);
else continue;
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

Try this one. I have also optimise the code (you only need to check upto sqrt(i) ).
var prime = [];
prime.push(2); //smallest prime
var flag = 0;
for(var i = 3; i < 100; i=i+2) //skip all even no
{
for(var j = 3; j*j <= i; j=j+2) //check by upto sqrt(i), skip all even no
{
if(i % j == 0) {
flag = 0;break; //not a prime, break
}
flag = 1;
}
if (flag == 1) prime.push(i); //prime, add to answer
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

Because you blank your list of primes EVERY loop cycle, move it outside the for loop

You need to make your variable prime outside of your loop
This is the code you have re-written
var prime = [];
for(var i = 2; i < 100; i++)
{
for(var j = 0; j <= i; j++)
{
var p = i % j;
}
if(p != 0) prime.push(i);
else continue;
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

I'm a fan of the sieve of Eratosthenes.
The following code should do what you wanted.
var prime = Array(101).fill(true);
for (var i = 2; i < 100; ++i){
if (prime[i]){
document.writeln(i, "<br>");
for (var j = i*i; j < 100; j += i){
prime[j] = false;
}
}
}
Or since it's only up to 100 you could just manually type the list (but, hey where's the learning if you do it that way?).

(1) Move prime outside the for loop, (2) start j at 2 and end when j < i, (3) check when p == 0 with a boolean flag and break inner loop.
var prime = []; //put prime out here so it does not reassign
for(var i = 2; i < 100; i++)
{
var isPrime = true;
for(var j = 2; j < i; j++) //start j at 2
{
var p = i % j;
if(p == 0)
{
isPrime = false;
break;
}
}
if(isPrime) prime.push(i);
}
for(var k = 0; k < prime.length; k++)
{
document.writeln(prime[k], "<br>");
}

javascript matrix manipulation is not working

This is a bad coded solution to a problem in "advent of code": link to problem
I don't know the reason because my code is not working properly, I had an error related to regular expressions cause I didn't reset the pointer of the regexp object, now that error is fixed I think, but something is escaping to my knowledge in what I've done bad.
The problem is that the solution that my code displays is not correct, you can submit a solution on the link I've provided and get feedback of your solutions.
Correct solution: 543903
Given solution: 418954
// day 6 of advent of code
var input = "removed, take from problem";
function processInput(input, matrix) {
var linesOfInput = input.split("\n");
var matches;
var turnOnRE = /turn on (\d+),(\d+).*?(\d+),(\d+)/g;
var turnOffRE = /turn off (\d+),(\d+).*?(\d+),(\d+)/g;
var toggleRE = /toggle (\d+),(\d+).*?(\d+),(\d+)/g;
// regular expression objects lastIndex property must be 'reseted' in order to work well
for (var i = 0 ; i < linesOfInput.length; i++) {
turnOnRE.lastIndex = 0;
turnOffRE.lastIndex = 0;
toggleRE.lastIndex = 0;
matches = turnOnRE.exec(linesOfInput[i]);
if (matches != null) {
manipulateLights(matrix, matches[1], matches[2], matches[3], matches[4], true);
continue;
}
matches = turnOffRE.exec(linesOfInput[i]);
if (matches != null) {
manipulateLights(matrix, matches[1], matches[2], matches[3], matches[4], false);
continue;
}
matches = toggleRE.exec(linesOfInput[i]);
manipulateLights(matrix, matches[1], matches[2], matches[3], matches[4]);
}
}
function manipulateLights(matrix, startI, startJ, endI, endJ, newValue) {
if (newValue == undefined) { // toogle
for (var i = startI ; i <= endI; i++) {
for (var j = startJ ; j <= endJ; j++) {
matrix[i][j] = !matrix[i][j];
}
}
console.log(startI, startJ, endI, endJ, newValue);
} else {
for (var i = startI ; i <= endI; i++) {
for (var j = startJ ; j <= endJ; j++) {
matrix[i][j] = newValue;
}
}
console.log(startI, startJ, endI, endJ, newValue);
}
console.log(countTurnedOnLights(matrix));
}
function countTurnedOnLights(matrix) {
var turnedOn = 0;
for (var i = 0 ; i < matrixWidth; i++) {
for (var j = 0 ; j < matrixHeigth; j++) {
if (matrix[i][j] == true) {
turnedOn++;
}
}
}
return turnedOn;
}
var matrixHeigth = 1000;
var matrixWidth = 1000;
// define a bidimensional array, is almost like in C++
var lightMatrix = new Array(matrixWidth);
for (var i = 0 ; i < matrixWidth; i++) {
lightMatrix[i] = new Array(matrixHeigth);
}
// turn off all lights
for (var i = 0 ; i < matrixWidth; i++) {
for (var j = 0 ; j < matrixHeigth; j++) {
lightMatrix[i][j] = false;
}
}
processInput(input, lightMatrix);
console.log(countTurnedOnLights(lightMatrix));

OK I figured out the error - your regular expression matches are being treated as strings when you first create your for loops.
for (var i = startI ; i <= endI; i++) {
for (var j = startJ ; j <= endJ; j++) {
When you hit a combo like 756,53 through 923,339, it thinks 53 > 339 and it exits the loop immediately. Either wrap each "start" variable with Number() in your for loops, or do so when passing the parameters.

Array size 114467 good, 114468 not work

I have a strange problem with my alghoritm, which work if array size less than 114468 and doesn't work if more than 114468. Browse with google chrome. Can't understand why =\ Here is the code:
Generate array:
var arr = [];
var res = [];
for (var i = 114467; i > 0; i--) {
arr.push([i - 1, i]);
}
Find first elem in array to sort:
for (var i = 0, j = arr.length; i < j && res.length == 0; i++) {
var found = false;
for (var m = 0; m < j; m++) {
if (i == m || arr[i][0] == arr[m][1] || arr[i][1] == arr[m][0]) {
found = true;
break;
}
if (!found) {
res.push(arr[m]);
arr.splice(m, 1);
}
}
}
Sorting:
do {
for (var i = 0, j = arr.length; i < j; i++) {
var resLength = res.length - 1;
if (arr[i][1] == res[resLength][0] || arr[i][0] == res[resLength][1]) {
res.push(arr[i]);
arr.splice(i, 1);
break;
}
}
} while (arr.length > 0);
On the step sorting it stops to work.
All code:
var t = function () {
var arr = [];
var res = [];
for (var i = 114467; i > 0; i--) {
arr.push([i - 1, i]);
}
var startsec = new Date().getSeconds();
var startmilsec = new Date().getMilliseconds();
document.write(startsec + '.' + startmilsec + '<br>');
for (var i = 0, j = arr.length; i < j && res.length == 0; i++) {
var found = false;
for (var m = 0; m < j; m++) {
if (i == m || arr[i][0] == arr[m][1] || arr[i][1] == arr[m][0]) {
found = true;
break;
}
if (!found) {
res.push(arr[m]);
arr.splice(m, 1);
}
}
}
do {
for (var i = 0, j = arr.length; i < j; i++) {
var resLength = res.length - 1;
if (arr[i][1] == res[resLength][0] || arr[i][0] == res[resLength][1]) {
res.push(arr[i]);
arr.splice(i, 1);
break;
}
}
} while (arr.length > 0);
var stopsec = new Date().getSeconds();
var stopmilsec = new Date().getMilliseconds();
document.write(stopsec + '.' + stopmilsec + '<br>');
var executionTime = (stopsec - startsec).toString() + "s" + (stopmilsec - startmilsec).toString() + "'ms";
document.write(executionTime + '<br>');
} ();
Do i get my memory limit?

Alright, I isolated the problem. It seems that splice(0,1) slows down astronomically when the array size increases from 114467 to 114468.
Using this custom benchmark:
var t;
function startBench(){t=new Date().getTime();}
function stopBench(){console.log(new Date().getTime()-t);}
var arr=[];
for (var i = 114467; i > 0; i--) {
arr.push([i - 1, i]);
}
var arr2=[];
for (var i = 114468; i > 0; i--) {
arr2.push([i - 1, i]);
}
startBench();
for(i=0;i<1000;i++){
arr.splice(0,1);
}
stopBench();
startBench();
for(i=0;i<1000;i++){
arr2.splice(0,1);
}
stopBench();
I get 3 ms for 114467 and 2740ms for 114468 on Chrome (1000 iterations), but 170 each on Firefox. Maybe you ought to be using a different way to remove elements? Using a variant of bubble sort may work better.
I've submitted a bug report on this. Looking at the reply, it seems to be a valid bug. Hopefully it'll be fixed.