add tests and handle ties

src/main.rs

@@ -4,6 +4,12 @@ const VOTE_SEPARATOR: &str = "- Vote Separator -\n";
 const ANIME_SEPARATOR: &str = " | ";
 const VALUE_SEPARATOR: &str = ",";
 
+#[derive(PartialEq)]
+enum ElectionResult {
+    Winner((usize, usize), usize),
+    Tie,
+}
+
 fn main() {
     let args: Vec<String> = std::env::args().skip(1).collect();
     if args.len() != 1 {
@@ -48,6 +54,14 @@ fn select_winners(
     let mut r: Vec<((usize, usize), usize)> = Combinations::of_size(0..candidate_count, 2)
         .map(|v| (v[0], v[1]))
         .map(|c| single_election(c, votes))
+        // Remove ties
+        .filter_map(|m| {
+            if let ElectionResult::Winner(relation, margin) = m {
+                Some((relation, margin))
+            } else {
+                None
+            }
+        })
         .collect();
     r.sort_by_key(|e| e.1);
     let mut result = Vec::new();
@@ -60,7 +74,7 @@ fn select_winners(
     for _ in 0..amount_of_winners {
         let winner = (0..candidate_count)
             // Find new winners each time.
-            .filter(|c| !winners.contains(&c))
+            .filter(|c| !winners.contains(c))
             .map(|c| {
                 (
                     c,
@@ -85,7 +99,7 @@ fn select_winners(
 fn single_election(
     (candidate_a, candidate_b): (usize, usize),
     votes: &[Vec<usize>],
-) -> ((usize, usize), usize) {
+) -> ElectionResult {
     let (mut a_votes, mut b_votes): (usize, usize) = (0, 0);
     for vote in votes {
         if vote[candidate_a] == vote[candidate_b] {
@@ -98,15 +112,17 @@ fn single_election(
         }
     }
     if a_votes > b_votes {
-        (
+        ElectionResult::Winner(
             (candidate_a, candidate_b),
             a_votes.max(b_votes) - a_votes.min(b_votes),
         )
-    } else {
-        (
+    } else if a_votes < b_votes {
+        ElectionResult::Winner(
             (candidate_b, candidate_a),
             a_votes.max(b_votes) - a_votes.min(b_votes),
         )
+    } else {
+        ElectionResult::Tie
     }
 }
 
@@ -125,11 +141,41 @@ mod tests {
     use super::*;
 
     #[test]
-    fn connection_test() {
+    fn connection() {
         let graph = [(0, 1), (1, 2), (0, 2), (2, 3)];
         assert!(connection_exists(&graph, (0, 3)));
         assert!(!connection_exists(&graph, (3, 0)));
         let graph = [(0, 1)];
         assert!(!connection_exists(&graph, (3, 0)));
     }
+
+    #[test]
+    fn votes() {
+        let candidates = ["Alice", "Bob", "Carol", "Dave"];
+        let votes: Vec<Vec<usize>> = vec![
+            vec![5, 4, 1, 0],
+            vec![5, 3, 2, 0],
+            vec![4, 5, 1, 0],
+            vec![5, 4, 0, 1],
+            vec![4, 3, 2, 0],
+            vec![5, 2, 1, 0],
+            vec![3, 5, 2, 0],
+        ];
+        let winners = select_winners(&votes, candidates.len(), candidates.len());
+        assert!(winners[0] == 0);
+        assert!(winners[3] == 3);
+
+        let candidates = ["Alice", "Bob", "Carol"];
+        let votes: Vec<Vec<usize>> = vec![
+            vec![5, 3, 1],
+            vec![5, 3, 1],
+            vec![3, 5, 1],
+            vec![3, 5, 1],
+            vec![1, 3, 5],
+            vec![1, 3, 5],
+            vec![5, 1, 3],
+        ];
+        let winners = select_winners(&votes, candidates.len(), candidates.len());
+        assert!(winners[0] == 1);
+    }
 }