I need to write a program that creates a 2d array in variable "numbers" in rows (5) and columns (4). The elements of the array have to be consecutive integers starting at 1 and end at 20. I have to use "for" loop.
[ 1, 2, 3, 4 ],
[ 5, 6, 7, 8 ],
[ 9, 10, 11, 12 ],
[ 13, 14, 15, 16 ],
[ 17, 18, 19, 20 ],
So I came up with that:
const numbers = [];
const columns = 4;
const rows = 5;
for (let i = 0; i < rows; i++) {
numbers [i] = [];
for (let j = 0; j < columns; j++){
numbers [i][j] = j + 1;
}
}
console.log(numbers);
But the result of this is five identical rows, like this:
[ 1, 2, 3, 4 ],
[ 1, 2, 3, 4 ],
[ 1, 2, 3, 4 ],
[ 1, 2, 3, 4 ],
[ 1, 2, 3, 4 ]
Do you have any idea how to fix it? How to make second row starting from 5?
Here is some updated code. You need to add i*columns to every value
const numbers = [];
const columns = 4;
const rows = 5;
for (let i = 0; i < rows; i++) {
numbers[i] = [];
for (let j = 0; j < columns; j++){
numbers[i][j] = j + 1 + (i*columns);
}
}
console.log(numbers);
Looks like in the second loop, you should do numbers [i][j] = j * i; instead
Every time the outer for loop starts a new iteration, j is reset back to 0, which is why you keep getting rows starting with 1.
To fix this, you could declare a variable outside of the for loops that tracks the current number, and use that instead of j like so:
const numbers = [];
const columns = 4;
const rows = 5;
let currNum = 0;
for (let i = 0; i < rows; i++) {
numbers [i] = [];
for (let j = 0; j < columns; j++){
currNum++;
numbers [i][j] = currNum;
}
}
console.log(numbers);
I have the following code in VS Code js file and running it through windows command prompt :
var arr = [
[1, 2],
[3, 4],
[5, 6]
];
for (var i = 0; i < arr.length; i++) {
for (var j = 0; j < arr.length; j++) {
console.log(arr[i][j]);
}
}
How come its giving me as an output :
1
2
undefined
3
4
undefined
5
6
undefined
Where does the undefined come from ? This doesnt happen when running it say on the FreeCodeCamp IDE
Thank you!
You are not considering length on inner arrays.
In the second for loop, you should be considering the length of each array item. In your existing example, 3 x 3 iterations are taking place hence you are seeing 9 values in the log.
var arr = [
[1, 2],
[3, 4],
[5, 6]
];
for (var i = 0; i < arr.length; i++) {
for (var j = 0; j < arr[i].length; j++) {
console.log(arr[i][j]);
}
}
the error lies within your second loop condition :j < arr.length should be j < arr[i].length
I know various ways to sort an array, but when the thing comes like i will have to manage time and space complexity i just don’t know what to do how to do
Help me to sort an array in better way with less time and space complexity
Assuming like i have 10k elements in an array and i will have to sort that array, which sorting algorithm will be better?
var Arr = [ 3, 4,1,2, 5,7];
Arr.sort((a,b)=> a-b);
console.log('Arr.sort------',Arr);//[ 1, 2, 3, 4, 5, 7 ]
OR
for (var i = 1; i < Arr.length; i++){
console.log('i:',i)
for (var j = 0; j < i; j++){
console.log(j)
if (Arr[i] < Arr[j]) {
var x = Arr[i];
Arr[i] = Arr[j];
Arr[j] = x;
}
}
}
console.log('sort------',Arr);//[ 1, 2, 3, 4, 5, 7 ]
OR
function selectionSort(arr) {
var minIdx, temp,
len = arr.length;
for (var i = 0; i < len; i++) {
minIdx = i;
for (var j = i + 1; j < len; j++) {
if (arr[j] < arr[minIdx]) {
minIdx = j;
}
}
temp = arr[i];
arr[i] = arr[minIdx];
arr[minIdx] = temp;
}
return arr;
}
var selectionSortArr=Arr
var ddd = selectionSort(selectionSortArr);
console.log('sort -------',selectionSortArr);//[ 1, 2, 3, 4, 5, 7 ]
I am attempting to do this Kata - https://www.codewars.com/kata/organize-a-round-robin-tournament/train/javascript.
The task is to create a function that organizes a round robin tournament.
Example:
buildMatchesTable(4)
Should return a matrix like:
[
[[1,2], [3, 4]], // first round: 1 vs 2, 3 vs 4
[[1,3], [2, 4]], // second round: 1 vs 3, 2 vs 4
[[1,4], [2, 3]] // third round: 1 vs 4, 2 vs 3
]
So far I have listed all possible matchups, but my code to put them in the correct format is incorrect, throwing the error "Cannot read property '0' of undefined".
I would greatly appreciate all responses as dumbed down as possible as I am new to this. Thanks a mil.
function buildMatchesTable(numberOfTeams) {
let pairs = [];
let n = numberOfTeams;
let arr = [];
//create all possible pairs without repeating
for (var i = 1; i <= n; i++){
for (var j = i+1; j <= n; j++){
pairs.push([i,j]);
}
}
//not working
for (var i = 0; i < (n-1); i++){
for (var j = 0; j < pairs.length; j++){
for (var k = 0; k < 2; k++){
if (!arr[i][j][k].includes(pairs[j][0]) && !arr[i][j][k].includes(pairs[j][1])){
arr[i][j].push(pairs[j]);
pairs.splice(j,1);
}
}
}
}
}
buildMatchesTable(6)
I am new to JavaScript, and I have an array which contains numbers.
var arr = [2,4,8,1,5,9,3,7,6];
How can I sort it using a native for loop in JavaScript?
I know sort function is available, but I want it through for loop.
The output should be:
var res = [1,2,3,4,5,6,7,8,9];
var Arr = [1, 7, 2, 8, 3, 4, 5, 0, 9];
for (var i = 1; i < Arr.length; i++)
for (var j = 0; j < i; j++)
if (Arr[i] < Arr[j]) {
var x = Arr[i];
Arr[i] = Arr[j];
Arr[j] = x;
}
console.log(Arr);
I would do something like this...
var input = [2,3,8,1,4,5,9,7,6];
var output = [];
var inserted;
for (var i = 0, ii = input.length ; i < ii ; i++){
inserted = false;
for (var j = 0, jj = output.length ; j < jj ; j++){
if (input[i] < output[j]){
inserted = true;
output.splice(j, 0, input[i]);
break;
}
}
if (!inserted)
output.push(input[i])
}
console.log(output);
Maybe there are more efficient ways, but if you want to use the for loop, it's my first idea...
First create an empty array where the sorted numbers will be pushed into.
let sorted = [];
Secondly, create a very large amount of numbers that none of the numbers of the array can match. This number will be used for the very first comparison to determine which number of the array is smaller.
let comparison = 9000000000;
Create a for loop.
This loop will have another loop inside of it. The inner loop will check for the smallest number in a given array, and once the smallest number is gotten, it will be push into the empty array we created. The smallest number will also be removed from the initial array and then the array will run again.
for(a = 0; a < arr.length; a++){
//This inner loop fetches the smallest number.
for(b = 0; b < arr.length; a++){
if(comparison > arr[b]){
comparison = arr[b];
}
}
// The smallest number is assigned to comparison
// Now it being pushed to the empty array
sorted.push(comparison);
// Remove the smallest number from the initial array
let indexOfSmallNumber = arr.indexOf(comparison);
arr.splice(indexOfSmallNumber, 1);
// Set the comparison back to 9000000000;
comparison = 90000000000;
a = -1;
// Here, "a" is our main loop index counter and we are
// setting it to -1 because we don't want it to change
// to 2 by default, doing this will make the loop run
// forever until the initial array is empty.
}
let arr = [4, 2, 5, 1]
let temp;
function converter(arr) {
for(let i=0; i<arr.length; i++) {
for (let j=i+1; j<arr.length; j++) {
if(arr[i] > arr[j]) {
temp = arr[i]
arr[i] = arr[j]
arr[j] = temp
}
}
}
return arr
}
const newArr = converter(arr)
console.log(newArr)
Use:
let s = [4, 6, 3, 1, 2];
for (let i = 0; i < s.length;) {
if (s[i] > s[i + 1]) {
let a = s[i];
s[i] = s[i + 1];
s[i + 1] = a;
i--;
}
else {
i++;
}
}
This is a sorting algorithm which has a best time complexity of O(n) and the worst time of O(n^2).
This code checks for each number, and then compares to all numbers on the left side.
To check the time it takes each code to run, you can also use this code below:
let start = process.hrtime.bigint()
let end = process.hrtime.bigint()
console.log(end - start) // This measures the time used in nano seconds.
Also for microseconds, you can use this performance.now().
Here there is a very simple solution that uses a temporary array to store the values greater than the current one. Then it puts the current value between the lesser and the greater values:
var arr = [2,4,8,1,5,9,3,7,6];
var res = [];
for (const c of arr) {
let tmp = [];
while (c < res[res.length-1]) {
tmp.unshift(res.pop());
}
res = [...res, c, ...tmp];
}
const numberArr = [5, 9, 2, 8, 4, 10, 1, 3, 7, 6];
function sortedFunction(arr) {
let sortedArr = [];
for (let i = 0; i < arr.length; i++) {
for (let j = i + 1; j < arr.length; j++) {
let n = 0;
if (arr[i] > arr[j]) {
n = arr[i];
arr[i] = arr[j];
arr[j] = n;
}
}
sortedArr.push(arr[i]);
}
return sortedArr;
}
sortedFunction(numberArr);
Under the JavaScript array sort section of W3Schools it talks about how to compare a value in an array with the others and then order them based on the values being returned. I updated the code to use a for loop to sort values.
// Ascending points
var points = [5.0, 3.7, 1.0, 2.9, 3.4, 4.5];
var output = [];
var i;
for (i = 0; i < points.length; i++) {
points.sort(function (a, b) {
return a - b
});
output += points[i] + "<br>";
}
console.log(output);
// Descending points
var points = [5.0, 3.7, 1.0, 2.9, 3.4, 4.5];
var output = [];
var i;
for (i = 0; i < points.length; i++) {
points.sort(function (a, b) {
return b - a
});
output += points[i] + "<br>";
}
console.log(output);
const array = [12, 3, 45, 61, 23, 45, 6, 7];
function sortArray(array) {
for (var i = 0; i < array.length; ++i) {
for (var j = 0; j < array.length - 1 - i; ++j) {
if (array[j] > array[j + 1]) {
[array[j], array[j + 1]] = [array[j + 1], array[j]];
}
}
}
return array;
}
console.log(sortArray(array));
Here are the two solutions for the same algorithm:
Solution 1:
We can directly use JavaScript functions:
let arr = [2, 4, 8, 1, 5, 9, 3, 7, 6]
const changeOrder = (arr) => {
return arr.sort((a, b) => a - b)
}
let result = changeOrder(arr);
console.log(result) // [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
Solution 2:
We can use a JavaScript for loop for doing the same
let arr = [2, 4, 8, 1, 5, 9, 3, 7, 6]
const changeOrder = (arr) => {
for(let i=1; i< arr.length; i++) {
for(let j=0; j < i; j++) {
if(arr[i] < arr[j]) {
let x = arr[i]
arr[i] = arr[j]
arr[j] = x
}
}
}
return arr;
}
let result = changeOrder(arr);
console.log(result) // [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
An improvement to previous answer
for (let i = 0; i < arr.length; i++) {
for (let j = 0; j < arr.length - i - 1; j++) {
if (arr[j] > arr[j + 1]) {
let temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
}
}