using splice inside 2D Array in Javascript - javascript

I've created this 2D array, and I'm trying to delete the rows that are having 5 "ones" or more,
I tried it with splice (a.splice(j,1)) but it doesn't work . I think because when using this method it changes the whole quantity of rows and that's affects the for loops.
Is it because I don't use splice correctly or should I use different method ?
Thanks !
a = Array(7).fill(0).map(x => Array(10).fill(0))
for (let i = 0; i < 5; i++) {
a[1][i + 2] = 1;
a[4][i + 2] = 1;
a[5][i + 2] = 1;
}
console.log(a);
let count = 0;
for (let j = 0; j < 7; j++) {
for (let i = 0; i < 10; i++) {
if (a[j][i] == 1) {
count = count + 1;
}
}
if (count > 4) {
console.log("Line" + j);
// a.splice(j,1);
}
count = 0;
// a.splice(j,1);
}

Your splice is correct but you move forward through the array (j is incremented). To do this type of operation you need to move backward through the array (j is decremented) - this way the changing array indices don't intefere with your loop.
See the example below:
a = Array(7).fill(0).map(x => Array(10).fill(0))
for (let i=0; i<5; i++) {
a[1][i+2] = 1;
a[4][i+2] = 1;
a[5][i+2] = 1;
}
console.log("Original array");
console.log(a);
for (let j = a.length - 1; j > 0; j--) {
var count;
for (let i = 0; i < a[j].length; i++) {
if (a[j][i] === 1) {
count += 1
}
}
if (count > 4) {
a.splice(j, 1);
}
count = 0;
}
console.log("Filtered array");
console.log(a);

Related

Fill matrix with snake pattern using javascript

I want to fill in a 2D array of numbers with snake pattern, I tried this algorithm but the result it's not the expected:
function fill2d(c,l) {
var arr = new Array[l][c];
let counter = 0;
for (let col = 0; col < arr.l; col++) {
if (col % 2 == 0) {
for (let row = 0; row < arr.l; row++) {
arr[row][col] = counter++;
}
} else {
for (let row = arr.length - 1; row >= 0; row--) {
arr[row][col] = counter++;
}
}
}
return arr;
}
fill2d(4,4)
some thing like that :
1 2 3 4
8 7 6 5
9 10 11 12
16 15 14 13
Okay so basically all you need is to traverse row-by-row but alternating between left-to-right and right-to-left. Here's my solution:
function fill2d(c, l) {
let arr = new Array(l);
for (var i = 0; i < l; i++) {
arr[i] = new Array(c);
}
let count = 1;
for (let i = 0; i < l; i++) {
console.log("i: ", i);
let right_to_left = i % 2;
for (let j = (right_to_left * (l - 1));
(right_to_left ? (j >= 0) : (j < c)); j += (right_to_left ? -1 : 1)) {
console.log("j: ", j);
arr[i][j] = count++;
}
}
return arr;
}
console.log(fill2d(4, 4));
Also, you weren't allocating a 2d array properly, you need to allocate a 1d array first and then allocate an array for each of the elements of that array.
Note: I added logs for each i and j so that you can see how the array is traversed.

Why does function reassign 2Darray argument as sideeffect from calling the latter

When I run the third line alone and log test2darr it returns a 2D array filled with 6's in a 3x3 matrix
But when I run the fourth line and log test2darr again, it returns:
[4, 5, 4]
​
[5, 6, 5]​
[4, 5, 4]
(as well as for secondtest)
Though it should return the same array of 6's for test2darr and on assign the 2d array to secondtest
const n = 3;
const filler = new Array(n * n);
const test2darr = fill2DarrFromArr(filler.fill(6));
const secondtest = pileReduce(test2darr);
Here is my code for fill2DarrFromArr and pileReduce:
function pileReduce(_cells) {
_cells = fillEmpty(_cells);
for (let j = 0; j < _cells.length; j++) { //The Algorithm itself is not important
for (let i = 0; i < _cells.length; i++) { // But there might be some assignment problem that I missed
if (_cells[j][i] >= 4) {
_cells[j][i] = _cells[j][i] - 4;
if (j !== _cells.length - 1) _cells[j + 1][i]++;
if (j !== 0) _cells[j - 1][i]++;
if (i !== _cells.length - 1) _cells[j][i + 1]++;
if (i !== 0) _cells[j][i - 1]++;
}
}
}
return _cells;
}
function fill2DarrFromArr(_arr) {
let sideLength = Math.sqrt(_arr.length);
let out = create2DArr(sideLength, sideLength);
for (let j = 0; j < sideLength; j++) {
for (let i = 0; i < sideLength; i++) {
out[j][i] = _arr[j * sideLength + i];
}
}
return out;
}
function create2DArr(_n, _m) {
let _arr = new Array(_n);
for (let j = 0; j < _m; j++) {
_arr[j] = new Array(_m);
}
return _arr;
}
function fillEmpty(_arr) {
for (let j = 0; j < _arr.length; j++) {
for (let i = 0; i < _arr.length; i++) {
if (!_arr[j][i]) _arr[j][i] = 0;
}
}
return _arr;
}
Passing an array into a function doesn't create a copy of that array. Your functions are modifying the contents of the passed arrays, therefore they have side effects.

How many times needed to Sort a number in an Array Javascript

I want to count how many times needed for an array to be sorted
var array = [4,2,3,1]
var yourCounter = 0;
for (var i = 0; i < array.length; i++) {
for (var j = 1; j < array.length-j; j++)
if (array[j - 1] > array[j]) {
yourCounter++;
} }
it will return 4 , it should be 5
but if I input array [1,2,3] will correctly return 0 , and if I input array [3,2,1] it will correctly return 3
You could take the given code and swap the values while counting.
for (int i = 0; i < n; i++) {
for (int j = 0; j < n - 1; j++) {
// Swap adjacent elements if they are in decreasing order
if (a[j] > a[j + 1]) {
swap(a[j], a[j + 1]);
}
}
}
var array = [4, 2, 3, 1],
counter = 0,
i, j, n = array.length;
for (i = 0; i < n; i++) {
for (j = 0; j < n - 1; j++) {
if (array[j] > array[j + 1]) {
[array[j + 1], array[j]] = [array[j], array[j + 1]];
++counter;
}
}
}
console.log(counter);
console.log(array);
I found the solution
var a = [4,2,3,1]
function sortArray(a){
let swapCount = 0;
let swapOccurred = true;
let index = 0;
while (swapOccurred == true && index < a.length){
swapOccurred == false;
if (a[index] > a[index+1]){
let holder = a[index]
a[index] = a[index+1];
a[index+1] = holder;
swapOccurred == true;
swapCount ++;
index = -1;
}
index ++
}
function countSwaps(a) {
let swapCount = 0;
[a, swapCount] = sortArray(a)
console.log(swapCount)
}
return [a, swapCount]
}

Creating a function to combine a nested array without recursion

I have the following array as an example;
let arr = [['red','blue','pink],['dog','cat','bird'],['loud', 'quiet']]
I need to write a generalized function that prints all combinations of one word from the first vector, one word from the second vector, etc. I looked up some codes on here but they are all recursion or working only with the specific array. How can I write this code without recursion?
let allComb = function(arr) {
if (arr.length == 1) {
return arr[0];
} else {
let result = [];
let arrComb = allComb(arr.slice(1));
for (let i = 0; i < arrComb.length; i++) {
for (let j = 0; j < arr[0].length; j++) {
result.push(arr[0][j] + ' ' + arrComb[i]);
}
}
return result;
}
}
allComb(arr)
This version uses a single increment per cycle technique with no recursion.
let arr = [
['red', 'blue', 'pink'],
['dog', 'cat', 'bird'],
['loud', 'quiet']
];
function allComb(arr) {
var total = 1;
var current = [];
var result = [];
for (var j = 0; j < arr.length; j++) {
total *= arr[j].length;
current[j] = 0;
}
for (var i = 0; i < total; i++) {
var inc = 1;
result[i] = "";
for (var j = 0; j < arr.length; j++) {
result[i] += arr[j][current[j]] + ' ';
if ((current[j] += inc) == arr[j].length)
current[j] = 0;
else
inc = 0;
}
}
return (result);
}
console.log(allComb(arr));
You may do as follows;
var arr = [['red','blue','pink'],['dog','cat','bird'],['loud', 'quiet']],
res = arr.reduce((p,c) => p.reduce((r,x) => r.concat(c.map(y => x + " " + y)),[]));
console.log(res);

How to program Pascal's Triangle in Javascript - confusion re Arrays

I'm having a little trouble with my attempt at this problem. Code Below:
function pasc(n){
var result = [[1]];
for (var row = 1; row < n; row++){
for (var col = 1; col <= row; col++){
result[row][col] = result[row - 1][col] + result[row - 1][col - 1];
}
}
return result;
}
pasc(10)
for (var i = 0; i < result.length; i++){
document.write(result[i]+"<br>");
}
It seems the problem hinges on assigning values to an array using an expression like myArray[1][1] = "foo"
I'm confused about this because I can do this: var myArray = []; myArray[4] = "foo" which seems to suggest that an element can be created at an arbitrary position in a 1 dimensional array, but not with 2 dimensions.
Any help with clearing up my misconceptions appreciated.
The Pascal's Triangle can be printed using recursion
Below is the code snippet that works recursively.
We have a recursive function pascalRecursive(n, a) that works up till the number of rows are printed. Each row is a element of the 2-D array ('a' in this case)
var numRows = 10,
triangle,
start,
stop;
// N is the no. of rows/tiers
// a is the 2-D array consisting of the row content
function pascalRecursive(n, a) {
if (n < 2) return a;
var prevRow = a[a.length-1];
var curRow = [1];
for (var i = 1; i < prevRow.length; i++) {
curRow[i] = prevRow[i] + prevRow[i-1];
}
curRow.push(1);
a.push(curRow);
return pascalRecursive(n-1, a); // Call the function recursively
}
var triangle = pascalRecursive(numRows, [[1]]);
for(var i = 0; i < triangle.length; i++)
console.log(triangle[i]+"\n");
JavaScript doesn't have two-dimensional arrays. What it does have is arrays that happen to contain other arrays. So, yes, you can assign a value to any arbitrary position in an array, and the array will magically make itself big enough, filling in any gaps with 'undefined'... but you can't assign a value to any position in a sub-array that you haven't explicitly created yet. You have to assign sub-arrays to the positions of the first array before you can assign values to the positions of the sub-arrays.
Replacing
for (var row = 1; row < n; row++){
for (var col = 1; col <= row; col++){
with
for (var row = 1; row < n; row++){
result[row] = [];
for (var col = 1; col <= row; col++){
should do it. Assuming all of your indexing logic is correct, anyway. You've got some problems there, too, since your initial array only contains a single value, so result[row][col] = result[row - 1][col] + result[row - 1][col - 1]; is accessing at least one cell that has never been defined.
Thanks Logan R. Kearsley. I have now solved it:
function pasc(n){
var result = [];
result[0] = [1];
result[1] = [1,1];
for (var row = 2; row < n; row++){
result[row] = [1];
for (var col = 1; col <= row -1; col++){
result[row][col] = result[row-1][col] + result[row-1][col-1];
result[row].push(1);
}
}
return result;
}
for (var i = 0; i < pasc(10).length; i++){
document.write(pasc(10)[i]+"<br>");
console.log(pasc(10)[i]+"<br>");
}
you can create Pascal's triangle using below code:
function pascal(n) {
var arr = [];
if (n == 1) {
arr[0] = [];
arr[0][0] = 1;
} else if (n == 2) {
arr[0] = [];
arr[0][0] = 1;
arr[1] = [];
arr[1][0] = 1;
arr[1][1] = 1;
} else if (n > 2) {
arr[0] = [];
arr[1] = [];
arr[0][0] = 1;
arr[1][0] = 1;
arr[1][1] = 1;
for (i = 2; i < n; i++) {
arr[i] = [];
arr[i][0] = 1;
for (j = 1; j < i; j++) {
arr[i][j] = arr[i - 1][j - 1] + arr[i - 1][j];
}
arr[i][j] = 1;
}
}
console.log(arr);
for (i = 0; i < arr.length; i++) {
console.log(arr[i].join(' '))
}
}
function pascal(n) {
var arr = [];
if (n == 1) {
arr[0] = [];
arr[0][0] = 1;
} else if (n == 2) {
arr[0] = [];
arr[0][0] = 1;
arr[1] = [];
arr[1][0] = 1;
arr[1][1] = 1;
} else if (n > 2) {
arr[0] = [];
arr[1] = [];
arr[0][0] = 1;
arr[1][0] = 1;
arr[1][1] = 1;
for (i = 2; i < n; i++) {
arr[i] = [];
arr[i][0] = 1;
for (j = 1; j < i; j++) {
arr[i][j] = arr[i - 1][j - 1] + arr[i - 1][j];
}
arr[i][j] = 1;
}
}
console.log(arr);
for (i = 0; i < arr.length; i++) {
console.log(arr[i].join(' '))
}
}
pascal(5)
This function will calculate Pascal's Triangle for "n" number of rows. It will create an object that holds "n" number of arrays, which are created as needed in the second/inner for loop.
function getPascalsTriangle(n) {
var arr = {};
for(var row = 0; row < n; row++) {
arr[row] = [];
for(var col = 0; col < row+1; col++) {
if(col === 0 || col === row) {
arr[row][col] = 1;
} else {
arr[row][col] = arr[row-1][col-1] + arr[row-1][col];
}
}
}
return arr;
}
console.log(getPascalsTriangle(5));
Floyd triangle
You can try the following code for a Floyd triangle
var prevNumber=1,i,depth=10;
for(i=0;i<depth;i++){
tempStr = "";j=0;
while(j<= i){
tempStr = tempStr + " " + prevNumber;
j++;
prevNumber++;
}
console.log(tempStr);
}
You can create arbitrary 2d arrays and store it in there and return the correct Pascal.
JavaScript does not have a special syntax for creating multidimensional arrays. A common workaround is to create an array of arrays in nested loops.
source
Here is my version of the solution
function pascal(input) {
var result = [[1], [1,1]];
if (input < 0) {
return [];
}
if (input === 0) {
return result[0];
}
for(var j = result.length-1; j < input; j++) {
var newArray = [];
var firstItem = result[j][0];
var lastItem = result[j][result[j].length -1];
newArray.push(firstItem);
for (var i =1; i <= j; i++) {
console.log(result[j][i-1], result[j][i]);
newArray.push(sum(result[j][i-1], result[j][i]));
}
newArray.push(lastItem);
result.push(newArray);
}
return result[input];
}
function sum(one, two) {
return one + two;
}
Here is the code i created for pascal triangle in javascript
'use strict'
let noOfCoinFlipped = 5
let probabiltyOfnoOfHead = 2
var dataStorer = [];
for(let i=0;i<=noOfCoinFlipped;i++){
dataStorer[i]=[];
for(let j=0;j<=i;j++){
if(i==0){
dataStorer[i][j] = 1;
}
else{
let param1 = (j==0)?0:dataStorer[i-1][j-1];
let param2 = dataStorer[i-1][j]?dataStorer[i-1][j]:0;
dataStorer[i][j] = param1+param2;
}
}
}
let totalPoints = dataStorer[noOfCoinFlipped].reduce((s,n)=>{return s+n;})
let successPoints = dataStorer[noOfCoinFlipped][probabiltyOfnoOfHead];
console.log(successPoints*100/totalPoints)
Here is the link as well
http://rextester.com/TZX59990
This is my solve:
function pascalTri(n){
let arr=[];
let c=0;
for(let i=1;i<=n;i++){
arr.push(1);
let len=arr.length;
if(i>1){
if(i>2){
for(let j=1;j<=(i-2);j++){
let idx=(len-(2*i)+j+2+c);
let val=arr[idx]+arr[idx+1];
arr.push(val);
}
c++;
}
arr.push(1);
}
}
return arr;
}
let pascalArr=pascalTri(7);
console.log(pascalArr);
here is the pattern for n = 3
#
##
###
here is js code to print this.
function staircase(n) {
for(var i=0 ; i<n ; i++) {
for(var j=n-1 ; j>i ; j--)
process.stdout.write(" ");
for(var k=0 ; k<=i; k++) {
process.stdout.write("#");
}
process.stdout.write("\n");
}
}
class PascalTriangle {
constructor(n) {
this.n = n;
}
factoriel(m) {
let result = 1;
if (m === 0) {
return 1;
}
while (m > 0) {
result *= m;
m--;
}
return result;
}
fill() {
let arr = [];
for (let i = 0; i < this.n; i++) {
arr.push([]);
}
for (let i = 0; i < arr.length; i++) {
for (let j = 0; j <= i; j++) {
arr[i].push(this.factoriel(i) / (this.factoriel(j) * this.factoriel(i - j)));
}
}
return arr;
}
}
var m = prompt("enter number:");
var arrMain = new Array();
for (var i = 0; i < m; i++) {
arrMain[i] = [];
}
for (var i = 0; i < m; i++) {
if (i == 0) {
arrMain[i] = [1];
} else if (i == 1) {
(arrMain[i]) = [1, 1];
} else {
for (var j = 0; j <= i; j++) {
if (j == 0 || j == arrMain[i - 1].length) {
arrMain[i][j] = 1;
} else {
arrMain[i][j] = arrMain[i - 1][j] + arrMain[i - 1][j - 1];
}
}
}
document.write(arrMain[i] + "<br>");
}
This is my take on this problem by gaining access to the previous row.
const generate = numRows => {
const triangle = [[1]]
for (let i = 1; i < numRows; i++) {
// Previous row
const previous = triangle[i - 1]
// Current row
const current = new Array(i + 1).fill(1)
// Populate the current row with the previous
// row's values
for (let j = 1; j < i; j++) {
current[j] = previous[j - 1] + previous[j]
}
// Add to triangle result
triangle.push(current)
}
return triangle
}

Categories

Resources