trie_rcv

Ranked Choice Voting (RCV) implementation using Tries in Rust
RCV differs from normal first past the post voting in that voters are allowed to rank candidates from most to least preferable. To determine the winner of an RCV election, the least votes for the least popular candidate(s) are transferred to their next choice until some candidate reaches a majority.

Example usage:

use trie_rcv;
use trie_rcv::RankedChoiceVoteTrie;
use trie_rcv::vote::VoteStruct;

fn main() {
    let votes = VoteStruct::from_vectors(&vec![
        vec![1, 2, 3, 4],
        vec![1, 2, 3],
        vec![3],
        vec![3, 2, 4],
        vec![4, 1]
    ]).unwrap();

    let rcv = RankedChoiceVoteTrie::new();
    let winner = rcv.run_election(votes);
    println!("WINNER = {:?}", winner);
    assert_eq!(winner, Some(1));
}

This implementation also supports votes containing withhold and abstain votes, where the withhold vote allows the voter to declare for none of the candidates, and the abstain vote allows the voter to voluntarily remove himself from the poll (this is useful for improving the chances that the rest of the votes are able to conclude with a winning candidate)

use trie_rcv;
use trie_rcv::RankedChoiceVoteTrie;
use trie_rcv::vote::{VoteStruct, SpecialVotes};

fn main() {
    let votes = VoteStruct::from_vectors(&vec![
        vec![1, SpecialVotes::WITHHOLD.to_int()],
        vec![2, 1],
        vec![3, 2],
        vec![3]
    ]).unwrap();

    let rcv = RankedChoiceVoteTrie::new();
    let winner = rcv.run_election(votes);
    println!("WINNER = {:?}", winner);
    assert_eq!(
        winner, None, concat![
        "Candidate 1's vote should not count after round 1, ",
        "no one should have majority"
    ]);
}

Build instructions

Build crate using cargo build, run integration tests with cargo test