Quick Sort(Hoare’s Partition) Visualization using JavaScript

Last Updated : 25 Feb, 2021

GUI(Graphical User Interface) helps in better understanding than programs. In this article, we will visualize Quick Sort using JavaScript. We will see how the array is being partitioned into two parts and how we get the final sorted array. We will also visualize the time complexity of Quick Sort.

Reference:

Approach:

First, we will generate a random array using Math.random() function.
Different colors are used to indicate which elements are compared, left partition and right partition.
Since the algorithm performs the operation very fast, the setTimeout() function has been used to slow down the process.
New array can be generated by pressing the “Ctrl+R” key.
The sorting is performed using QuickSort() function using hoare_partition() function

Example:

Before Sorting

After Sorting

Below is the program to visualize the Quick Sort algorithm.

index.html

<!DOCTYPE html> 
<html lang="en"> 
  
<head> 
    <link rel="stylesheet" href="style.css" /> 
</head> 
  
<body> 
    <br /> 
    <p class="header">Quick Sort (Hoare's Partition)</p> 
  
  
    <div id="array"></div> 
    <div id="count"></div> 
    <br /> 
    <h2 class="range" style="text-align: center"></h2> 
  
    <script src="script.js"></script> 
</body> 
  
</html>

style.css

* { 
    margin: 0px; 
    padding: 0px; 
    box-sizing: border-box; 
} 
  
.header { 
    font-size: 20px; 
    text-align: center; 
} 
  
#array { 
    background-color: white; 
    height: 288px; 
    width: 598px; 
    margin: auto; 
    position: relative; 
    margin-top: 64px; 
} 
  
.block { 
    width: 28px; 
    background-color: #6b5b95; 
    position: absolute; 
    bottom: 0px; 
    transition: 0.2s all ease; 
} 
  
.block_id { 
    position: absolute; 
    color: black; 
    margin-top: -20px; 
    width: 100%; 
    text-align: center; 
} 
  
.block_id2 { 
    position: absolute; 
    color: black; 
    margin-top: 22px; 
    width: 100%; 
    text-align: center; 
} 
  
.block2 { 
    width: 28px; 
    background-color: darkgray; 
    position: absolute; 
    transition: 0.2s all ease; 
} 
  
.block_id3 { 
    position: absolute; 
    color: black; 
    margin-top: 1px; 
    width: 100%; 
    text-align: center; 
} 
  
#count { 
    height: 20px; 
    width: 598px; 
    margin: auto; 
}

script.js

var container = document.getElementById("array"); 
  
// Function to generate the array of blocks 
function generatearray() { 
    for (var i = 0; i < 20; i++) { 
        // Return a value from 1 to 100 (both inclusive) 
        var value = Math.ceil(Math.random() * 100); 
  
        // Creating element div 
        var array_ele = document.createElement("div"); 
  
        // Adding class 'block' to div 
        array_ele.classList.add("block"); 
  
        // Adding style to div 
        array_ele.style.height = 
        `${value * 3}px`; 
        array_ele.style.transform =  
        `translate(${i * 30}px)`; 
  
        // Creating label element for displaying 
        // size of particular block 
        var array_ele_label =  
        document.createElement("label"); 
        array_ele_label.classList.add("block_id"); 
        array_ele_label.innerText = value; 
  
        // Appending created elements to index.html 
        array_ele.appendChild(array_ele_label); 
        container.appendChild(array_ele); 
    } 
} 
  
// Function to generate indexes 
var count_container = document.getElementById("count"); 
  
function generate_idx() { 
    for (var i = 0; i < 20; i++) { 
        // Creating element div 
        var array_ele2 = document.createElement("div"); 
  
        // Adding class 'block2' to div 
        array_ele2.classList.add("block2"); 
  
        // Adding style to div 
        array_ele2.style.height = 
        `${20}px`; 
        array_ele2.style.transform = 
        `translate(${i * 30}px)`; 
  
        //adding indexes 
        var array_ele_label2 =  
        document.createElement("label"); 
        array_ele_label2.classList.add("block_id3"); 
        array_ele_label2.innerText = i; 
  
        // Appending created elements to index.html 
        array_ele2.appendChild(array_ele_label2); 
        count_container.appendChild(array_ele2); 
    } 
} 
  
async function hoare_partition(l, r, delay = 700) { 
    var blocks =  
    document.querySelectorAll(".block"); 
    var pivot =  
    Number(blocks[l].childNodes[0].innerHTML); 
  
    var i = l - 1; 
    var j = r + 1; 
  
    while (true) { 
        // Find leftmost element greater than 
        // or equal to pivot 
        do { 
            i++; 
            if (i - 1 >= l) blocks[i - 1].style.backgroundColor = "red"; 
            blocks[i].style.backgroundColor = "yellow"; 
            //To wait for 700 milliseconds 
            await new Promise((resolve) => 
                setTimeout(() => { 
                    resolve(); 
                }, delay) 
            ); 
        } while (Number(blocks[i].childNodes[0].innerHTML) < pivot); 
  
        // Find rightmost element smaller than 
        // or equal to pivot 
        do { 
            j--; 
            if (j + 1 <= r) blocks[j + 1].style.backgroundColor = "green"; 
            blocks[j].style.backgroundColor = "yellow"; 
            //To wait for 700 milliseconds 
            await new Promise((resolve) => 
                setTimeout(() => { 
                    resolve(); 
                }, delay) 
            ); 
        } while (Number(blocks[j].childNodes[0].innerHTML) > pivot); 
  
        // If two pointers met. 
        if (i >= j) { 
            for (var k = 0; k < 20; k++) blocks[k].style.backgroundColor = "#6b5b95"; 
            return j; 
        } 
  
        //swapping ith and jth element 
        var temp1 = blocks[i].style.height; 
        var temp2 = blocks[i].childNodes[0].innerText; 
        blocks[i].style.height = blocks[j].style.height; 
        blocks[j].style.height = temp1; 
        blocks[i].childNodes[0].innerText = blocks[j].childNodes[0].innerText; 
        blocks[j].childNodes[0].innerText = temp2; 
        //To wait for 700 milliseconds 
        await new Promise((resolve) => 
            setTimeout(() => { 
                resolve(); 
            }, delay) 
        ); 
    } 
} 
  
// Asynchronous QuickSort function 
async function QuickSort(l, r, delay = 100) { 
    // QuickSort Algorithm 
    if (l < r) { 
        //Storing the index of pivot element after partition 
        var pivot_idx = await hoare_partition(l, r); 
        //Recursively calling quicksort for left partition 
        await QuickSort(l, pivot_idx); 
        //Recursively calling quicksort for right partition 
        await QuickSort(pivot_idx + 1, r); 
    } 
} 
  
// Calling generatearray function 
generatearray(); 
  
// Calling generate_idx function 
generate_idx(); 
  
// Calling QuickSort function 
QuickSort(0, 19);

Output:

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