🎓 How Ranked Choice Voting Works

The Problem with Normal Voting

In a normal election with 5 candidates, someone can win with just 21% of the vote. That means 79% of people didn't want the winner. This is called the spoiler effect - similar candidates split their supporters' votes.

How RCV Fixes This

Instead of picking just one option, you rank all options from favorite to least favorite. Then the algorithm simulates multiple rounds of voting.

Walkthrough: 10 Voters, 4 Options

Imagine 10 students voting on the next project:

Notice: Snake Game had the most first-choice votes, but Chat App was the most broadly acceptable choice. That's the power of RCV.

The Algorithm (Pseudocode)

function ranked_choice_vote(ballots):
    active_candidates = all candidates

    while true:
        # Count first-choice votes
        counts = {}
        for ballot in ballots:
            first_active = first candidate in ballot
                           that is still active
            if first_active exists:
                counts[first_active] += 1

        total = sum of all counts
        threshold = floor(total / 2) + 1

        # Check for winner
        for candidate in counts:
            if counts[candidate] >= threshold:
                return candidate  # WINNER!

        # No winner - eliminate last place
        loser = candidate with min(counts)
        remove loser from active_candidates

        # Votes automatically redistribute
        # next loop iteration

Why RCV Matters

def run_rcv(candidates: dict[int, str],
            ballots: list[list[int]]) -> int | None:
    """
    candidates: {1: "Snake Game", 2: "Chat App", ...}
    ballots: [[2, 1, 3], [1, 3, 2], ...]
             each ballot is candidate IDs in preference order

    Returns: winning candidate ID, or None
    """
    pass  # Your code here!