Sorting Algorithm Visualization : Quick Sort

An algorithm like Quicksort algorithm is hard to understand theoretically. We can understand easily by visualizing such kind of algorithms. In this article, a program that visualizes the Quicksort Algorithm has been implemented.
The Graphical User Interface(GUI) is implemented in python using pygame library.
Approach:

  • An array of random values is generated and are drawn as lines(bars) in the window.
  • Since the algorithm performs the operation very fast, pygame.time.delay() has been used to slow down the process.
  • Assign specific keys for each operation (start sorting, reset bars).
  • The actions are performed using ‘pygame.event.get()’ method, which stores all the events which user performs.
  • Different colors are used to indicate types of bar.
    • Green – Unsorted bar
    • Blue – Pivot bar
    • Orange – Sorted bar

Examples:

Input:
Press “Enter” key to Perform Visualization.
Press “r” key to generate new array.
Output:
Initial:

Sorting:

Final:

Please make sure to install the pygame library in your system.

Below is the implementation of the above visualizer:

Python

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# Python implementation of the 
# Sorting visualiser: Quick Sort
  
# Imports
import pygame
import random
pygame.font.init()
  
# Total window
screen = pygame.display.set_mode(
            (900, 650)
        )
  
# Title and Icon 
pygame.display.set_caption("SORTING VISUALISER")
  
# Uncomment below lines for setting 
# up the icon for the visuliser
# img = pygame.image.load('sort_icon.png')
# pygame.display.set_icon(img)
  
# Boolean variable to run 
# the program in while loop
run = True
  
# Window size and some initials
width = 900
length = 600
array =[0]*151
arr_clr =[(0, 204, 102)]*151
clr_ind = 0
clr =[(0, 204, 102), (255, 0, 0),\
      (0, 0, 153), (255, 102, 0)]
fnt = pygame.font.SysFont("comicsans", 30)
fnt1 = pygame.font.SysFont("comicsans", 20)
  
  
# Function to generate new Array
def generate_arr():
    for i in range(1, 151):
        arr_clr[i]= clr[0]
        array[i]= random.randrange(1, 100)
          
# Intially generate a array
generate_arr() 
  
# Function to refill the 
# updates on the window
def refill():
    screen.fill((255, 255, 255))
    draw()
    pygame.display.update()
    pygame.time.delay(30)
      
# Sorting Algo:Quick sort
def quicksort(array, l, r):
    if l<r:
        pi = partition(array, l, r)
        quicksort(array, l, pi-1)
        refill()
        for i in range(0, pi + 1):
            arr_clr[i]= clr[3]
        quicksort(array, pi + 1, r)
          
# Function to partition the array
def partition(array, low, high):
    pygame.event.pump() 
    pivot = array[high]
    arr_clr[high]= clr[2]
    i = low-1
    for j in range(low, high):
        arr_clr[j]= clr[1]
        refill()
        arr_clr[high]= clr[2]
        arr_clr[j]= clr[0]
        arr_clr[i]= clr[0]
        if array[j]<pivot:
            i = i + 1
            arr_clr[i]= clr[1]
            array[i], array[j]= array[j], array[i]
    refill()
    arr_clr[i]= clr[0]
    arr_clr[high]= clr[0]
    array[i + 1], array[high] = array[high], array[i + 1
      
    return ( i + 1 )
      
# Function to Draw the 
# array values
def draw():
    # Text should be rendered
    txt = fnt.render("SORT : PRESS 'ENTER'",\
                       1, (0, 0, 0))
      
    # Position where text is placed
    screen.blit(txt, (20, 20))
    txt1 = fnt.render("NEW ARRAY : PRESS 'R'",\
                      1, (0, 0, 0))
    screen.blit(txt1, (20, 40))
    txt2 = fnt1.render("ALGORITHM USED: QUICK SORT",\
                       1, (0, 0, 0))
    screen.blit(txt2, (600, 60))
    element_width =(width-150)//150
    boundry_arr = 900 / 150
    boundry_grp = 550 / 100
    pygame.draw.line(screen, (0, 0, 0),\
                (0, 95), (900, 95), 6)
      
    # Drawing the array values as lines
    for i in range(1, 151):
        pygame.draw.line(screen,\
                arr_clr[i], (boundry_arr * i-3, 100),\
                (boundry_arr * i-3,\
                 array[i]*boundry_grp + 100),\
                 element_width)
                   
# Program should be run
# continuously to keep the window open
while run:
    # background
    screen.fill((255, 255, 255))
      
    # Event handler stores all event 
    for event in pygame.event.get():
          
        # If we click Close button in window
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_r:
                generate_arr() 
            if event.key == pygame.K_RETURN:
                quicksort(array, 1, len(array)-1)     
    draw()
    pygame.display.update()
      
pygame.quit()

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Output:


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