Souvenir's Booth - Algorithm Design and Analysis Project Presentation

Souvenir’s Booth
USING AUTO COMPLETE
By: Abhinav Garg (101303004) | Akshit Arora (101303012) | Chahak Gupta (101303041)
(Analysis and Design of Algorithms (UCS 501) Project)
Submitted To - Ms. Tarunpreet Bhatia

Project Introduction
• Autocomplete, is a feature in which an application predicts the rest
of a word a user is typing. In graphical user interfaces, users can
press the tab key to accept a suggestion or the down arrow key to
accept one of several.
• It speeds up human-computer interactions when it correctly predicts
words being typed. It works best in domains with a limited number
of possible words.
• The project focuses on studying different approaches to generate
strings with the prefix entered by the user.

Objective
1. To optimize auto-completion of the word.
2. To optimize depth first search by improving the traversal of data
structure by special algorithm and analysis techniques.
3. To search word in trie.
4. Modify the default structure of trie and with certain tweaks
improve the overall time complexity.
5. We substantially increased the number of word in the Trie from 4
to 45000 words and it worked correctly.

Algorithm Techniques Used
1. For printing all possible words in a trie with given root:
Backtracking Traversal (similar to DFS)
2. For searching the prefix in trie: naïve algorithm used
3. For insertion of new words in trie: Recursion

Structure of Node used in the project

Pseudocode -1 (Trie, C++)
suggest(key, pos, * root){
if(root->ptrs[key[pos]] != NULL){
suggest(key,pos+1,root->ptrs[key[pos]])
else
printall(root)
SOUVENIR_BOOTH(file, key, len)
string word
node *root
open file("wordlist.txt")
while(end of file)
word<-getword_from_file
insertword(word,0,root)
close file
if(len<=0)
return -1
suggest(key,0,root)
if(found)
print “no words found”
return

Pseudocode – 1 (Trie, C++)
InsertWord(word,pos,*root) {
If word.length()=pos
root->Word <- word
return
if root-> ptrs[word[pos]] IS NULL
newnode <- new node
newnode->info <- word[pos]
root->ptrs[word[pos]] <- newnode
insertword(word,pos+1,root->ptrs[word[pos]])
else
insertword(word,pos+1,root->ptrs[word[pos]])
printall(* root){
for i<-0 to 255
if(root->ptrs[i]!=NULL){
printall (root->ptrs[i])
if(root->Word != "" AND (root->Word.length() = len AND
len!=-9999))
print root->Word
else if(root->Word != "" AND len = -9999)
Print root->Word
found <- 1

Results and Screenshots
Figure 1: Output when user doesn't know length Figure 2: Output when user inputs non-positive length
Figure 3: Output when
specified length matches

Results and Screenshots
Figure 4: The dictionary

Asymptotic Analysis (Space complexity)
In worst case analysis, the dictionary will consist of words with no
common prefix. At every level, 256 combinations will be possible
from each node. So this will result in a lot of memory usage.
Maximum number of nodes possible at level 1=256;
Maximum number of nodes possible at level 2=2562 …
Maximum number of nodes possible at level m=256m
Maximum total number of nodes in a trie with m as maximum length
of word will be:
256+2562+2563+2564+……………. 256m
= (256(256m+1 – 1) )/( 256-1)
= (256/255) (256m+1 – 1) = O(256m)

Asymptotic Analysis (Time Complexity)
1. The key determines trie’s depth.
2. Using trie, we can search / insert the single key in O(M) time.
Here, M is maximum string length.
3. In this project, we get the search result in O(key_length + ∑(L)),
where key_length is input given by user and ∑(L) is summation of
all the string lengths starting with prefix entered by user.

Souvenir's Booth - Algorithm Design and Analysis Project Presentation

Conclusions
1. Souvenir’s Booth problem of finding the desired solution was
solved.
2. Auto complete was successfully implemented using Trie.
3. Suggests words if words of desired length are not available.
4. DFS and Trie's implementation was understood.

Achievements
Autocomplete speeds up human-computer interactions when it correctly predicts words being typed.
It works best in domains with a limited number of possible words (such as in command line
interpreters), when some words are much more common (such as when addressing an e-mail), or
writing structured and predictable text (as in source code editors).
Can be used for:
1. Web browsers: filling similar fields
2. E-mail programs: auto fill email
3. Search engines: Based on search history
4. Word Processors: auto correct
5. IDEs: syntax correction and highlighting
6. Mobiles: Typing most commonly used words

References
Topcoder Tutorials: https://www.topcoder.com/community/data-
science/data-science-tutorials/using-tries/
Bhavin’s Blog (Directi): http://bhavin.directi.com/to-trie-or-not-to-
trie-a-comparison-of-efficient-data-structures/
Wikipedia – Autocomplete and Trie data structure articles
Geeks for Geeks: http://www.geeksforgeeks.org/trie-insert-and-
search/

Souvenir's Booth - Algorithm Design and Analysis Project Presentation

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