Optimize intersection

election/agreement.go

@@ -75,15 +75,15 @@ func (a *Agreement) TallyList() ([]uuid.UUID, error) {
 	return list, nil
 }
 
-func MaxSubset(t int, ballotLists []BallotList) map[string]bool {
-	n := len(ballotLists)
+func MaxSubset(t int, superset []BallotList) map[string]bool {
+	n := len(superset)
 	combis := combin.Combinations(n, t)
 	log.Printf("N: %d, combis: %d\n", n, len(combis))
 	subsets := make([]map[string]bool, len(combis), n)
 	for i, ls := range combis {
 		sets := make([]BallotList, 0, len(ls))
 		for _, i := range ls {
-			sets = append(sets, ballotLists[i])
+			sets = append(sets, superset[i])
 		}
 		subsets[i] = Intersection(sets)
 	}
@@ -97,15 +97,16 @@ func MaxSubset(t int, ballotLists []BallotList) map[string]bool {
 }
 
 func Intersection(superset []BallotList) map[string]bool {
-	section := make(map[string]int, len(superset[0]))
-	for _, set := range superset {
-		for hash := range set {
-			section[hash]++
-		}
-	}
 	set := make(map[string]bool)
-	for hash, num := range section {
-		if num >= len(superset) {
+	for hash := range superset[0] {
+		good := true
+		for _, set := range superset {
+			if _, ok := set[hash]; !ok {
+				good = false
+				break
+			}
+		}
+		if good {
 			set[hash] = true
 		}
 	}