Used 'unique append' to ensure that a transition can only contain a given state once

main.go

@@ -147,8 +147,13 @@ func thompson(re string) *State {
 			s3.transitions = make(map[int][]*State)
 			s3.output = append(s3.output, s1.output...)
 			s3.output = append(s3.output, s2.output...)
-			s3.transitions[s1.content] = append(s3.transitions[s1.content], s1)
-			s3.transitions[s2.content] = append(s3.transitions[s2.content], s2)
+			// Unique append is used here (and elsewhere) to ensure that,
+			// for any given transition, a state can only be mentioned once.
+			// For example, given the transition 'a', the state 's1' can only be mentioned once.
+			// This would lead to multiple instances of the same set of match indices, since both
+			// 's1' states would be considered to match.
+			s3.transitions[s1.content] = unique_append(s3.transitions[s1.content], s1)
+			s3.transitions[s2.content] = unique_append(s3.transitions[s2.content], s2)
 			s3.content = EPSILON
 			s3.isEmpty = true