Related
I've written a merge sort visualisation in p5.js which shows the steps of merge sort. This works fine as a sequential visualisation, but I'd quite like to show this as a true representation, where you can see each part of the array being sorted at the same time (with multiple sections being visualised sorting at the same time, to truly reflect the recursion). The code itself is relatively simple:
// Split the array recursively
let mid = Math.floor((right + left) / 2);
if (right - left < 1) {
return;
}
// My attempt to visualise this properly
await Promise.all([mergeSortSlice(array, left, mid), mergeSortSlice(array, mid + 1, right)]);
// THIS WORKS, but only for sequential sorting
// await mergeSortSlice(array, left, mid);
// await mergeSortSlice(array, mid + 1, right)
// Putting sleep(200) here also works, but doesn't show the steps of the sort as they are happening, just the result of each stage of the sort.
leftCounter = 0;
rightCounter = 0;
l = left;
r = mid + 1;
valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
while (rightCounter < rightArray.length && leftCounter < leftArray.length) {
if (leftArray[leftCounter] < rightArray[rightCounter]) {
array.splice(l + rightCounter, 1);
array.splice(valuesStartIndex, 0, leftArray[leftCounter]);
l++;
leftCounter++;
valuesStartIndex++;
await sleep(200);
} else {
array.splice(r, 1);
array.splice(valuesStartIndex, 0, rightArray[rightCounter]);
r++;
rightCounter++;
valuesStartIndex++;
await sleep(200);
}
}
The problem with using Promise.all is that the split parts of the array are getting mixed up, I believe due to the recursion? This is resulting in the array not getting sorted properly.
My timeout function:
async function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
The setup function and draw loop:
let values = [50, 10, 80, 56, 30, 25, 15]
function setup() {
createCanvas(600, 190);
frameRate(60);
mergeSort(values)
}
function draw() {
rectWidth = 10;
background(23);
stroke(0);
fill(255);
for (let i = 0; i < values.length; i++) {
rect(i * rectWidth, height - values[i], rectWidth, values[i]);
}
}
The combination of async functions and recursion makes it difficult for me to come up with a solution for this. Any help/advice would be much appreciated.
You were actually very close to having a working solution. Your issue is that you are creating a bunch of global variables inside your mergeSortSlice function:
// These were all missing the let keyword
// And were therefore either assigning or implicitly declaring
// globally scoped variables.
let leftCounter = 0;
let rightCounter = 0;
let l = left;
let r = mid + 1;
let valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
When two instances of a function invocation being run as part of a Promise each of which await on timeouts, their execution is going to be interleaved (which you want so you can graphically represent the theoretical parallelism). However, when those functions alter global variables this is a classic shared memory multi-threading bug.
Here's an adaptation of your code with the bug fixed, highlighting added, and a slightly different delay strategy:
function merge_sort(p) {
const Mode = {
Shuffling: 0,
Sorting: 1
};
const spacing = 5;
let array = [...Array(40)].map((_, i) => i);
let highlights = [];
let itemWidth;
let itemHeight;
let currentMode = Mode.Shuffling;
let iterator;
let frameRate = 8;
let redrawPromise;
let signalRedraw;
p.setup = function() {
p.createCanvas(p.windowWidth, p.windowHeight);
p.frameRate(frameRate * 5);
itemWidth = (p.width - (spacing * (array.length + 1))) / array.length;
itemHeight = p.height - spacing * 2;
iterator = shuffle();
initRedrawPromise();
};
function initRedrawPromise() {
redrawPromise =
new Promise(resolve => {
signalRedraw = resolve;
});
redrawPromise.then(() => initRedrawPromise());
}
p.draw = function() {
p.background('white');
// draw
for (let i = 0; i < array.length; i++) {
if (highlights[i]) {
p.fill(highlights[i]);
} else {
p.fill('blue');
}
let fractionalHeight = (array[i] + 1) / array.length;
let pixelHeight = fractionalHeight * itemHeight;
p.rect(
(i + 1) * spacing + i * itemWidth,
spacing + (itemHeight - pixelHeight),
itemWidth,
pixelHeight
);
}
signalRedraw();
if (currentMode === Mode.Shuffling) {
// update
let next = iterator.next();
if (next.value) {
// Done suffle, switch to sort
currentMode = Mode.Sorting;
p.frameRate(frameRate);
sort().then(() => {
// switch back to shuffling
currentMode = Mode.Shuffling;
p.frameRate(frameRate * 5);
iterator = shuffle();
});
}
}
};
p.keyPressed = function(e) {
if (e.key === 'ArrowRight' || e.key === 'ArrowUp') {
frameRate++;
p.frameRate(frameRate);
} else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') {
frameRate = Math.max(0, frameRate - 1);
p.frameRate(frameRate);
}
}
// shuffle the array. yield false for each step where the array is not yet shuffled. yield true once the array is shuffled.
function* shuffle() {
// for each position in the array (except the last position),
// if the chosen item is not the current item, swap the two items.
for (let i = 0; i < array.length - 1; i++) {
highlight(i);
yield false;
let j = randomInt(i, array.length);
if (j !== i) {
highlight(i, j);
yield false;
swap(i, j);
highlight(j, i);
yield false;
} else {
highlight(i);
yield false;
}
}
yield true;
}
function sort() {
highlights = [];
return sortSlice(0, array.length - 1);
}
async function sortSlice(left, right) {
if (right - left < 1) {
return;
}
// Split the array recursively
let mid = Math.floor((right + left) / 2);
await Promise.all([sortSlice(left, mid), sortSlice(mid + 1, right)]);
for (let ix = left; ix <= right; ix++) {
highlights[ix] = undefined;
}
let leftCounter = 0;
let rightCounter = 0;
let l = left;
let r = mid + 1;
let valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
while (rightCounter < rightArray.length && leftCounter < leftArray.length) {
if (leftArray[leftCounter] < rightArray[rightCounter]) {
array.splice(l + rightCounter, 1);
array.splice(valuesStartIndex, 0, leftArray[leftCounter]);
highlights[valuesStartIndex] = 'green';
highlights[r] = 'red';
l++;
leftCounter++;
valuesStartIndex++;
} else {
array.splice(r, 1);
array.splice(valuesStartIndex, 0, rightArray[rightCounter]);
highlights[valuesStartIndex] = 'green';
r++;
rightCounter++;
valuesStartIndex++;
highlights[l + rightCounter] = 'red';
}
// at each merge step wait for a redraw that shows this step
await redrawPromise;
highlights[valuesStartIndex - 1] = 'gray';
for (let ix = valuesStartIndex; ix <= right; ix++) {
highlights[ix] = undefined;
}
}
}
function swap(i, j) {
const tmp = array[i];
array[i] = array[j];
array[j] = tmp;
}
function randomInt(lowerBound, upperBound) {
return lowerBound + Math.floor(Math.random() * (upperBound - lowerBound));
}
function highlight(i, j) {
highlights = [];
if (i !== undefined) {
highlights[i] = 'green';
}
if (j !== undefined) {
highlights[j] = 'red';
}
}
}
sketch = new p5(merge_sort);
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.4.0/p5.js"></script>
I'm new to JavaScript, I'm trying to solve leetcode question 37. I need to a create a blank two dimensional array, I initially used the method in the comments; however, it doesn't work correctly, it will change all the value. Then, I used the for loop method to create array and currently it worked correctly. But I still cannot figured out why this will happen, could anyone explain the reason why this will happen, is this because of shallow copy?
var solveSudoku = function (board) {
// let rows = new Array(9).fill(new Array(10).fill(0)),
let rows = new Array(9);
for (let i = 0; i < 9; i++) {
rows[i] = new Array(10).fill(0);
}
let cols = new Array(9);
for (let i = 0; i < 9; i++) {
cols[i] = new Array(10).fill(0);
}
let boxes = new Array(9);
for (let i = 0; i < 9; i++) {
boxes[i] = new Array(10).fill(0);
}
// let cols = new Array(9).fill(new Array(10).fill(0)),
// boxes = new Array(9).fill(new Array(10).fill(0));
for (let i = 0; i < 9; i++) {
for (let j = 0; j < 9; j++) {
let c = board[i][j];
if (c !== '.') {
let n = parseInt(c),
bx = Math.floor(j / 3),
by = Math.floor(i / 3);
// 0代表为使用，1为使用过
rows[i][n] = 1;
console.log(i, n)
cols[j][n] = 1;
// box索引
boxes[by * 3 + bx][n] = 1;
}
}
}
fill(board, 0, 0)
function fill(board, x, y) {
// 完成填充条件
if (y === 9) return true;
// 下一个点的坐标
let nx = (x + 1) % 9,
// 判断进入是否下一行
ny = (nx === 0) ? y + 1 : y;
// 如果已经填充，则进入下一个点
if (board[y][x] !== '.') return fill(board, nx, ny);
// 没有被填充过
for (let i = 1; i <= 9; i++) {
let bx = Math.floor(x / 3),
by = Math.floor(y / 3),
box_key = by * 3 + bx;
if (!rows[y][i] && !cols[x][i] && !boxes[box_key][i]) {
rows[y][i] = 1;
cols[x][i] = 1;
boxes[box_key][i] = 1;
board[y][x] = i.toString();
console.log(board[y][x])
// 递归向下一个点求解
if (fill(board, nx, ny)) return true;
// 恢复初始状态
board[y][x] = '.';
boxes[box_key][i] = 0;
rows[y][i] = 0;
cols[x][i] = 0;
}
}
return false;
}
console.log(board);
};
The problem with fill(), at least with object, is that it passes the same object, by reference, to all element of the array. So if you mutate this object, then it will mutate every object of every arrays.
Note that in your case, you are creating a new Array object using it's constructor ( new Array() ) which makes them objects.
const matrix = new Array(5).fill(new Array(5).fill(0));
console.log(matrix);
In the previous snippet, you can see that the values of the other rows, from the second one to the end, are reference to the initial row.
To get around that, you can fill you array with empty values and then use the map() to create unique object for each position in the array.
const matrix = new Array(5).fill().map(function() { return new Array(5).fill(0); });
console.log(matrix);
As you can see in the previous snippet, all the rows are now their unique reference.
This is the reason all of your values were changed.
I've applied this solution to your code. I wasn't able to test it, because I wasn't sure of the initial parameters to pass.
I've also used anonymous function here ( function() { return; } ), but I would success using arrow function ( () => {} ) instead, if you are comfortable with them. It's cleaner.
var solveSudoku = function (board) {
let rows = new Array(9).fill().map(function() { return new Array(10).fill(0); }),
cols = new Array(9).fill().map(function() { return new Array(10).fill(0); }),
boxes = new Array(9).fill().map(function() { return new Array(10).fill(0); });
for (let i = 0; i < 9; i++) {
for (let j = 0; j < 9; j++) {
let c = board[i][j];
if (c !== '.') {
let n = parseInt(c),
bx = Math.floor(j / 3),
by = Math.floor(i / 3);
// 0代表为使用，1为使用过
rows[i][n] = 1;
console.log(i, n)
cols[j][n] = 1;
// box索引
boxes[by * 3 + bx][n] = 1;
}
}
}
fill(board, 0, 0)
function fill(board, x, y) {
// 完成填充条件
if (y === 9) return true;
// 下一个点的坐标
let nx = (x + 1) % 9,
// 判断进入是否下一行
ny = (nx === 0) ? y + 1 : y;
// 如果已经填充，则进入下一个点
if (board[y][x] !== '.') return fill(board, nx, ny);
// 没有被填充过
for (let i = 1; i <= 9; i++) {
let bx = Math.floor(x / 3),
by = Math.floor(y / 3),
box_key = by * 3 + bx;
if (!rows[y][i] && !cols[x][i] && !boxes[box_key][i]) {
rows[y][i] = 1;
cols[x][i] = 1;
boxes[box_key][i] = 1;
board[y][x] = i.toString();
console.log(board[y][x])
// 递归向下一个点求解
if (fill(board, nx, ny)) return true;
// 恢复初始状态
board[y][x] = '.';
boxes[box_key][i] = 0;
rows[y][i] = 0;
cols[x][i] = 0;
}
}
return false;
}
console.log(board);
};
I get convergence, nevertheless, the results are never the same when the algorithm is refreshed. This occurs even when the data observations is the same dataset. Can anyone tell me where my methodology is wrong? For the life of me I can't figure out where the process is wrong.
function kmeans2(k, data, canvas, converge) {
this.canvas = jsHS.GetDimensions(canvas);
this.k = k;
this.centroids = []; // Array of centroids
this.centroids2compare = [];
this.data = data;
this.converge = converge;
this.init();
}
kmeans2.prototype.distance = function () {
var dif = 0,
iArray = jsHS.isArray(arguments);
if (iArray) {
if (arguments.length > 2) {
for (var i = 0; i < arguments.length; i+2) {
var p0 = arguments[i],
p1 = arguments[i + 1];
dif += Math.pow(p0[0] - p1[0], 2);
dif += Math.pow(p0[1] - p1[1], 2);
}
}
else {
var pd0 = arguments[0],
pd1 = arguments[1];
dif += Math.pow(pd0[0] - pd1[0], 2);
dif += Math.pow(pd0[1] - pd1[1], 2);
}
}
return Math.sqrt(dif);
};
kmeans2.prototype.Means = function (Array) {
var bin = 0;
[].forEach.call(Array, function(a){
bin += a;
});
return bin / Array.length;
};
kmeans2.prototype.init = function () {
for (var l = 0; l < this.k; l++) {
var dataItem = this.data[Math.floor(Math.random() * this.data.length)];
this.centroids.push(dataItem);
}
for (var i = 0; i < this.centroids.length; i++) {
if (i > 0) {
var distance = this.distance(this.centroids[i], this.centroids[i - 1]);
console.log(distance);
}
}
this.clusterCentroids(); // return centroid center after calculating means.
};
kmeans2.prototype.clusterCentroids = function () {
var points0 = [];
this.centroids2compare = this.centroids;
// Find distances between centroid and observations.
for (var d = 0; d < this.data.length; d++) {
var cinbin = [];
for (var c0 = 0; c0 < this.k; c0++) {
var dis = this.distance(this.centroids[c0], this.data[d]);
cinbin.push({ 'cid': c0, 'distance': dis });
}
var minResult = cinbin.reduce((cid, obj) => {
return obj.distance < cid.distance ? obj : cid;
});
points0.push({ 'id': d, 'datapoint': this.data[d], 'centroid': minResult.cid });
}
// Assign observations their appropriate centroid.
var centroidBin = [];
for (var c = 0; c < this.k; c++) {
var cb = [];
for (var p = 0; p < points0.length; p++) {
if (c === points0[p].centroid) {
cb.push(points0[p]);
}
}
centroidBin.push(cb);
}
// Calculate the mean distance between centroids and its assigned observations.
this.centroids = [];
for (var bin = 0; bin < centroidBin.length; bin++) {
var xAxis = [],
yAxis = [],
cb0 = centroidBin[bin];
[].forEach.call(cb0, function (dp) {
xAxis.push(dp.datapoint[0]);
yAxis.push(dp.datapoint[1]);
});
var xMean = this.Means(xAxis);
var yMean = this.Means(yAxis);
this.centroids.push([xMean, yMean]);
}
// Test for convergence. If stored centroids equal new centroids then convergence is achieved.
if (JSON.stringify(this.centroids2compare) !== JSON.stringify(this.centroids)) {
this.centroids2compare = [];
points0 = [];
this.clusterCentroids();
}
else {
this.converge(centroidBin, this.centroids);
}
};
window['jsHS']['kmeans2'] = kmeans2;
Implementation
var k50 = new jsi.kmeans2(5, Array50, canvas, function (con, centroids) {
var count50 = 0;
var cmark = {
x: 0,
y: 0,
rad:0,
clr: null,
setArc: function () {
ctx.beginPath();
ctx.arc(this.x, this.y, this.rad, 0, Math.PI * 2, true);
ctx.fillStyle = this.clr;
ctx.fill();
}
};
[].forEach.call(centroids, (c) => {
cmark.x = c[0];
cmark.y = c[1];
cmark.clr = '#0B6623';
cmark.rad = 25;
cmark.setArc();
});
});
This example plots the centroids on a canvas area fine enough but when the browser refreshes the centroids change.
I haven't looked much at your code, but I know that the k-means algorithm tends to give different results when you run it several times. This is because it's highly dependent on where the first centroids (which are selected randomly) are located.
The algorithm can find a local minimum and get "stuck" there, and terminate.
There's no guarantee that you will find the global minimum the first time you run it.
This function shuffles only matrix[y], but I want it to shuffle matrix[y][x] But it doesn't want to shuffle correctly.
The code what I used:
function Shuffle(arguments) {
for (var k = 0; k < arguments.length; k++) {
var i = arguments[k].length;
if (i == 0)
return false;
else {
while (--i) {
var j = Math.floor(Math.random() * (i + 1));
var tempi = arguments[k][i];
var tempj = arguments[k][j];
arguments[k][i] = tempj;
arguments[k][j] = tempi;
}
return arguments;
}
}
return arguments
}
var matrix = [
];
var ab = 36;
for (var y = 0; y < ab; y++) {
matrix.push([])
for (var x = 0; x < ab; x++) {
matrix[y][x] = Math.floor(Math.random() * 1)
}
for (var x = 0; x < ab / 2; x++) {
matrix[y][x] = 1
}
}
arr = Shuffle(matrix);
console.log(arr)
var side = 16;
function setup() {
createCanvas(arr[0].length * side, arr.length * side);
background('#acacac');
frameRate()
}
function draw() {
for (var y = 0; y < arr.length; y++) {
for (var x = 0; x < arr[y].length; x++) {
if (matrix[y][x] == 0) {
fill(0, 255, 0)
rect(y * side, x * side, side, side)
} else if (matrix[y][x] == 1) {
fill("red")
rect(y * side, x * side, side, side)
} else if (matrix[y][x] == 2) {
fill(255, 255, 0)
rect(y * side, x * side, side, side)
} else if (matrix[y][x] == 3) {
fill(255, 0, 0)
rect(y * side, x * side, side, side)
}
}
}
}
So this function shuffles only matrix[y], but I want it to shuffle matrix[y][x].
Any ideas? Here is the screenshot:
.
As mentioned in comment, you had a return statement after the whileloop, causing the forloop to never finish as expected
function Shuffle(arguments) {
for (var k = 0; k < arguments.length; k++) {
var i = arguments[k].length;
if (i == 0)
return false;
else {
while (--i) {
var j = Math.floor(Math.random() * (i + 1));
var tempi = arguments[k][i];
var tempj = arguments[k][j];
arguments[k][i] = tempj;
arguments[k][j] = tempi;
}
return arguments; // remove this line
}
}
return arguments
}
You probably can transform this to a one dimensional array, then shuffle, then transform back. You just need to know how many rows you want.
const myArr = [[1,2],[3,4]];
const oneDimArr = myArr.reduce((a, b) => [...a, ...b], []);
const shuffledArr = Shuffle(oneDimArr); // this is your existing function
const shuffled2DimArr = shuffledArr.reduce((acc, i) => {
if(acc[acc.length-1].length >= 2) { // here we build 2 cols
acc.push([]);
}
acc[acc.length-1].push(i);
return acc;
}, [[]]);
I've got two arrays
var mp3 = ['sing.mp3','song.mp3','tune.mp3','jam.mp3',etc];
var ogg = ['sing.ogg','song.ogg','tune.ogg','jam.ogg',etc];
i need to shuffle both arrays so that they come out the same way, ex:
var mp3 = ['tune.mp3','song.mp3','jam.mp3','sing.mp3',etc];
var ogg = ['tune.ogg','song.ogg','jam.ogg','sing.ogg',etc];
there's a few posts on stackoverflow that shuffle arrays in different ways--this one is pretty great--but none of them demonstrate how to shuffle two arrays in the same exact way.
thnx!
Add an extra argument to the Fisher-Yates shuffle. (assumes that your arrays are equal length)
var mp3 = ["sing.mp3", "song.mp3"];
var ogg = ["sing.ogg", "song.ogg"];
function shuffle(obj1, obj2) {
var index = obj1.length;
var rnd, tmp1, tmp2;
while (index) {
rnd = Math.floor(Math.random() * index);
index -= 1;
tmp1 = obj1[index];
tmp2 = obj2[index];
obj1[index] = obj1[rnd];
obj2[index] = obj2[rnd];
obj1[rnd] = tmp1;
obj2[rnd] = tmp2;
}
}
shuffle(mp3, ogg);
console.log(mp3, ogg);
UPDATE:
If you are going to support more arrays (as suggested in the comments), then you could modify the Fisher-Yates as follows (aswell as perform some checks to make sure that the arguments are of Array and that their lengths match).
var isArray = Array.isArray || function(value) {
return {}.toString.call(value) !== "[object Array]"
};
var mp3 = ["sing.mp3", "song.mp3", "tune.mp3", "jam.mp3"];
var ogg = ["sing.ogg", "song.ogg", "tune.ogg", "jam.ogg"];
var acc = ["sing.acc", "song.acc", "tune.acc", "jam.acc"];
var flc = ["sing.flc", "song.flc", "tune.flc", "jam.flc"];
function shuffle() {
var arrLength = 0;
var argsLength = arguments.length;
var rnd, tmp;
for (var index = 0; index < argsLength; index += 1) {
if (!isArray(arguments[index])) {
throw new TypeError("Argument is not an array.");
}
if (index === 0) {
arrLength = arguments[0].length;
}
if (arrLength !== arguments[index].length) {
throw new RangeError("Array lengths do not match.");
}
}
while (arrLength) {
rnd = Math.floor(Math.random() * arrLength);
arrLength -= 1;
for (argsIndex = 0; argsIndex < argsLength; argsIndex += 1) {
tmp = arguments[argsIndex][arrLength];
arguments[argsIndex][arrLength] = arguments[argsIndex][rnd];
arguments[argsIndex][rnd] = tmp;
}
}
}
shuffle(mp3, ogg, acc, flc);
console.log(mp3, ogg, acc, flc);
From that example, simply add a second parameter (your second array) and perform the operation on both arrays. You will just need to add and use a second temp, so you aren't overwriting your temps.
This should do the trick ASSUMING THE ARRAYS ARE THE SAME LENGTH:
function shuffle(array, array2) {
var counter = array.length, temp, temp2, index;
// While there are elements in the array
while (counter > 0) {
// Pick a random index
index = Math.floor(Math.random() * counter);
// Decrease counter by 1
counter--;
// And swap the last element with it
temp = array[counter];
temp2 = array2[counter];
array[counter] = array[index];
array2[counter] = array2[index];
array[index] = temp;
array2[index] = temp2;
}
}
I would seriously consider restructuring the way you're keeping track of the information, but in general you can separate out the shuffle itself from the stuff being shuffled. You need a function to generate a random permutation, and then a function to apply a permutation to an array.
function shuffle(o) { //v1.0
for(var j, x, i = o.length; i; j = Math.floor(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
};
function permutation( length ) {
var p = [], i;
for (i = 0; i < length; ++i) p[i] = i;
return shuffle(p);
}
function permute( a, p ) {
var r = [];
for (var i = 0; i < a.length; ++i)
r.push(a[p[i]]);
for (i = 0; i < a.length; ++i)
a[i] = r[i];
}
Then you can create a single random permutation and apply it to any list (of the right length) you want.
var p = permutation( mp3.length );
permute(mp3, p);
permute(ogg, p);
permute(aac, p);
// etc
(Shuffle function taken from the SO question linked in the OP.)
If you have two arrays of length 2, #Xotic750s function always returns the same value. UseMath.round instead of Math.floor.
function shuffle_two_arrays_identically(arr1, arr2){
"use strict";
var l = arr1.length,
i = 0,
rnd,
tmp1,
tmp2;
while (i < l) {
rnd = Math.round(Math.random() * i)
tmp1 = arr1[i]
tmp2 = arr2[i]
arr1[i] = arr1[rnd]
arr2[i] = arr2[rnd]
arr1[rnd] = tmp1
arr2[rnd] = tmp2
i += 1
}}
<script>
var arrayList= ['a','b','c','d','e','f','g'];
arrayList.sort(function(){
return 0.5 - Math.random()
})
document.getElementById("output").innerHTML = arrayList;
<script>