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FPTPStrategy

The FPTPStrategy class implements the First Past The Post (FPTP) voting system, also known as simple plurality voting. In this system, voters select a single candidate, and the candidate with the most votes wins.

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Algorithm

FPTP uses a simple counting mechanism:
  1. Count the number of votes each candidate receives
  2. Sort candidates by vote count in descending order
  3. The candidate with the most votes is declared the winner
  4. If multiple candidates are tied for the top position, the tie is flagged for manual resolution

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Interface

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calculateResults

Calculates election results using the FPTP mechanism.
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ballots
Ballot[]
required
Array of all ballots cast in the election. Each ballot must contain a single candidate ID in its preferences array.
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candidates
Candidate[]
required
Array of all candidates participating in the election.
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results
VoteResult[]
Ordered array of vote results, sorted by vote count (descending). Each result contains:
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candidateID
string
Unique identifier of the candidate
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candidateName
string
Display name of the candidate
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votes
number
Total number of votes received
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percentage
number
Percentage of total votes (0-100)
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isWinner
boolean
True if this candidate won the election. False if tied or lost.
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isTied
boolean
True if multiple candidates are tied for first place. When true, isWinner will be false.

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Example

const strategy = new FPTPStrategy();

const candidates = [
  new Candidate('c1', 'e1', 'Alice Johnson', 'Progressive Party', 'Bio'),
  new Candidate('c2', 'e1', 'Bob Smith', 'Conservative Party', 'Bio'),
  new Candidate('c3', 'e1', 'Carol White', 'Independent', 'Bio')
];

const ballots = [
  new Ballot('b1', 'e1', ['c1']), // Vote for Alice
  new Ballot('b2', 'e1', ['c1']), // Vote for Alice
  new Ballot('b3', 'e1', ['c1']), // Vote for Alice
  new Ballot('b4', 'e1', ['c2']), // Vote for Bob
  new Ballot('b5', 'e1', ['c2']), // Vote for Bob
  new Ballot('b6', 'e1', ['c3'])  // Vote for Carol
];

const results = strategy.calculateResults(ballots, candidates);

// Results:
// [
//   { candidateID: 'c1', candidateName: 'Alice Johnson', votes: 3, percentage: 50, isWinner: true },
//   { candidateID: 'c2', candidateName: 'Bob Smith', votes: 2, percentage: 33.33, isWinner: false },
//   { candidateID: 'c3', candidateName: 'Carol White', votes: 1, percentage: 16.67, isWinner: false }
// ]

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validateBallot

Validates that a ballot is properly formed for FPTP voting.
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ballot
Ballot
required
The ballot to validate
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candidateCount
number
required
Number of candidates in the election (not used in FPTP validation)
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valid
boolean
Returns true if the ballot contains exactly one candidate preference, false otherwise.

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Validation Rules

  • The ballot must have a preferences array
  • The preferences array must contain exactly one candidate ID
  • Multiple selections or empty ballots are invalid

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Example

const strategy = new FPTPStrategy();

// Valid ballot
const validBallot = new Ballot('b1', 'e1', ['c1']);
strategy.validateBallot(validBallot, 3); // true

// Invalid: multiple preferences
const invalidBallot = new Ballot('b2', 'e1', ['c1', 'c2']);
strategy.validateBallot(invalidBallot, 3); // false

// Invalid: empty preferences
const emptyBallot = new Ballot('b3', 'e1', []);
strategy.validateBallot(emptyBallot, 3); // false

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Tie Handling

When multiple candidates receive the same highest number of votes:
  • All tied candidates have isTied: true
  • All tied candidates have isWinner: false
  • The tie must be resolved manually by election administrators
const ballots = [
  new Ballot('b1', 'e1', ['c1']),
  new Ballot('b2', 'e1', ['c1']),
  new Ballot('b3', 'e1', ['c2']),
  new Ballot('b4', 'e1', ['c2'])
];

const results = strategy.calculateResults(ballots, candidates);

// Both c1 and c2 tied with 2 votes each:
// results[0] = { ..., votes: 2, isWinner: false, isTied: true }
// results[1] = { ..., votes: 2, isWinner: false, isTied: true }

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Implementation Location

Source: ~/workspace/source/src/services/strategies/FPTPStrategy.ts:6-53

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