Table of Contents
- Problem Statement
- Assumptions
- Requirements
- Implementation Details
- Data Models
- Implementation Details
- CODE
Problem Statement
You are required to design and implement an online polling system. The system should allow users to create, manage, and participate in polls. Each poll consists of a question and multiple options for answers. Users can vote on polls and view the results.
Assumptions :
- We are usin a Class based implementation
- We are not using additional Database to store this information
- As not DB & server is involved, no REST API
- simple Low Level approch on Polling System
Requirements
Create Polls:
- Users should be able to create a new poll with a question and multiple answer options.
- Each poll must have a unique identifier, a question, a list of options, and a timestamp of creation.
Manage Polls:
- Users should be able to update the question or options of an existing poll.
- Users should be able to delete a poll.
Vote in Polls:
- Users should be able to cast a vote for one of the options in a poll.
- Each user can only vote once per poll.
View Poll Results:
- Users should be able to view the current results of a poll, including the number of votes for each option.
Poll Data:
- Store polls, options, and votes in a way that allows efficient retrieval and updates.
- Ensure data integrity and consistency, especially when multiple users are voting simultaneously.
Implementation Details
Functions/Methods:
Create Poll
createPoll :
-
Input:
question
(string),options
(array of strings) -
Output:
pollId
(string),message
(string) -
Example:
createPoll("What is your favorite color?", ["Red", "Blue", "Green", "Yellow"])
returns{"pollId": "123", "message": "Poll created successfully."}
Update Poll
updatePoll :
-
Input:
pollId
(string),question
(string),options
(array of strings) -
Output:
message
(string) -
Example:
updatePoll("123", "Updated question?", ["Option1", "Option2"])
returns{"message": "Poll updated successfully."}
Delete Poll
deletePoll :
-
Input:
pollId
(string) -
Output:
message
(string) -
Example:
deletePoll("123")
returns{"message": "Poll deleted successfully."}
Vote In Poll
voteInPoll :
-
Input:
pollId
(string),userId
(string),option
(string) -
Output:
message
(string) -
Example:
voteInPoll("123", "user1", "Option1")
returns{"message": "Vote cast successfully."}
View Poll Results
viewPollResults :
-
Input:
pollId
(string) -
Output:
pollId
(string),question
(string),results
(object with option keys and vote count values) -
Example:
viewPollResults("123")
returns{"pollId": "123", "question": "What is your favorite color?", "results": {"Red": 10, "Blue": 5, "Green": 3, "Yellow": 2}}
Data Models
- Poll:
{
"pollId": "123",
"question": "What is your favorite color?",
"options": ["Red", "Blue", "Green", "Yellow"],
"createdAt": "2024-07-11T00:00:00Z"
}
- Vote:
{
"pollId": "123",
"userId": "user1",
"option": "Red",
"timestamp": "2024-07-11T01:00:00Z"
}
Implementation Details
This code defines a basic polling system using JavaScript classes. It allows the creation, management, and voting in polls. Let's break down each part of the code:
1. Class Definitions
Poll
Class
- Purpose: Represents an individual poll.
-
Constructor Parameters:
-
id
: A unique identifier for the poll. -
question
: The question being asked in the poll. -
options
: An array of possible options that users can vote on.
-
-
Properties:
-
pollId
: Stores the unique ID of the poll. -
question
: Stores the poll question. -
options
: Stores the array of options. -
createdAt
: Stores the creation date and time of the poll.
-
Vote
Class
- Purpose: Represents an individual vote cast by a user.
-
Constructor Parameters:
-
pollId
: The ID of the poll the vote is associated with. -
userId
: The ID of the user who cast the vote. -
option
: The option that the user voted for.
-
-
Properties:
-
pollId
: Stores the poll ID for which the vote was cast. -
userId
: Stores the user ID of the voter. -
option
: Stores the option that the user voted for. -
timestamp
: Stores the date and time when the vote was cast.
-
2. PollManager Class
Purpose: Manages the entire polling system, including creating polls, managing votes, and viewing results.
Constructor:
-
Properties:
-
polls
: AMap
that stores all polls, where the key is the poll ID and the value is thePoll
object. -
pollResults
: AMap
that stores the results of each poll, where the key is the poll ID and the value is anotherMap
that tracks votes for each option. -
userVotes
: AMap
that stores the votes by each user, where the key is the poll ID and the value is anotherMap
that tracks whether a user has voted in that poll.
-
Methods:
-
createPoll(question, options)
- Generates a new poll with a unique ID.
- Initializes the poll results, setting the vote count for each option to 0.
- Stores the poll and returns the generated poll ID.
-
updatePoll(pollId, question, options)
- Updates the question and options for an existing poll.
- Resets the poll results to 0 for the updated options.
- Returns a success message if the poll is found, otherwise returns "Poll not found."
-
deletePoll(pollId)
- Deletes a poll by its ID.
- Also removes associated poll results and user votes.
- Returns a success message if the poll is found, otherwise returns "Poll not found."
-
voteInPoll(pollId, userId, option)
- Allows a user to cast a vote in a specific poll.
- Ensures a user can only vote once per poll.
- Updates the vote count for the selected option if valid.
- Returns appropriate messages depending on whether the vote was successful, the user had already voted, or the poll or option was invalid.
-
viewPollResults(pollId)
- Returns the results of a specific poll in an array format, where each entry is a tuple of the option and its vote count.
- Returns "Poll not found" if the poll doesn't exist.
3. Example Usage
- Poll Creation: A poll is created asking, "What is your favorite color?" with options ["Red", "Blue", "Green", "Yellow"]. The poll ID is generated as "1".
- Voting: Multiple users vote in the poll, and the system ensures users can only vote once.
- Viewing Results: The poll results are displayed, showing the vote counts for each option.
- Updating the Poll: The poll's question and options are updated, resetting the results.
- Voting in Updated Poll: A user votes in the updated poll, and the results are displayed.
- Poll Deletion: The poll is deleted, and an attempt to view the results afterward confirms the poll no longer exists.
This implementation provides a basic but functional polling system, handling common scenarios such as poll creation, updating, voting, and deletion.
CODE
class Poll {
constructor(id, question, options) {
this.pollId = id;
this.question = question;
this.options = options;
this.createdAt = new Date();
}
}
class Vote {
constructor(pollId, userId, option) {
this.pollId = pollId;
this.userId = userId;
this.option = option;
this.timestamp = new Date();
}
}
class PollManager {
constructor() {
this.polls = new Map();
this.pollResults = new Map();
this.userVotes = new Map();
}
createPoll(question, options) {
const pollId = (this.polls.size + 1).toString();
const poll = new Poll(pollId, question, options);
this.polls.set(pollId, poll);
const result = new Map();
options.forEach(option => result.set(option, 0));
this.pollResults.set(pollId, result);
return pollId;
}
updatePoll(pollId, question, options) {
const poll = this.polls.get(pollId);
if (poll) {
poll.question = question;
poll.options = options;
// Update results for the new options
const result = new Map();
options.forEach(option => result.set(option, 0));
this.pollResults.set(pollId, result);
return "Poll updated successfully.";
}
return "Poll not found.";
}
deletePoll(pollId) {
if (this.polls.delete(pollId)) {
this.pollResults.delete(pollId);
this.userVotes.delete(pollId);
return "Poll deleted successfully.";
}
return "Poll not found.";
}
voteInPoll(pollId, userId, option) {
const poll = this.polls.get(pollId);
if (poll) {
if (!this.userVotes.has(pollId)) {
this.userVotes.set(pollId, new Map());
}
const userVote = this.userVotes.get(pollId);
if (userVote.get(userId)) {
return "User has already voted.";
}
const result = this.pollResults.get(pollId);
if (result.has(option)) {
result.set(option, result.get(option) + 1);
userVote.set(userId, true);
return "Vote cast successfully.";
} else {
return "Invalid option.";
}
}
return "Poll not found.";
}
viewPollResults(pollId) {
const results = this.pollResults.get(pollId);
if (results) {
return Array.from(results.entries());
}
return "Poll not found.";
}
}
// Example usage
const pollManager = new PollManager();
// Creating a poll
const pollId = pollManager.createPoll("What is your favorite color?", ["Red", "Blue", "Green", "Yellow"]);
console.log("Poll created with ID:", pollId);
// Voting in the poll
let voteMessage = pollManager.voteInPoll(pollId, "user1", "Red");
console.log(voteMessage);
voteMessage = pollManager.voteInPoll(pollId, "user2", "Blue");
console.log(voteMessage);
voteMessage = pollManager.voteInPoll(pollId, "user1", "Green");
console.log(voteMessage); // Should inform the user has already voted
// Viewing poll results
let results = pollManager.viewPollResults(pollId);
console.log("Poll results for poll ID", pollId, ":", results);
// Updating the poll
let updateMessage = pollManager.updatePoll(pollId, "What is your favorite primary color?", ["Red", "Blue", "Yellow"]);
console.log(updateMessage);
// Voting in the updated poll
voteMessage = pollManager.voteInPoll(pollId, "user3", "Yellow");
console.log(voteMessage);
// Viewing updated poll results
results = pollManager.viewPollResults(pollId);
console.log("Updated poll results for poll ID", pollId, ":", results);
// Deleting the poll
let deleteMessage = pollManager.deletePoll(pollId);
console.log(deleteMessage);
// Attempting to view results of a deleted poll
results = pollManager.viewPollResults(pollId);
if (typeof results === "string") {
console.log(results);
}
// Response
// Poll created with ID: 1
// Vote cast successfully.
// Vote cast successfully.
// User has already voted.
// Poll results for poll ID 1 : [['Red', 1], ['Blue', 1], ['Green', 0], ['Yellow', 0]]
// Poll updated successfully.
// Vote cast successfully.
// Updated poll results for poll ID 1 : [['Red', 0], ['Blue', 0], ['Yellow', 1]]
// Poll deleted successfully.
// Poll not found.
Note: Please follow for more detail & Enchanced version of this article with DB, API & other system Design Concept.
Low-Level Design: Polling System - API's Using Nodejs & SQL
Low-Level Design: Polling System - Edge Cases
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