# HG changeset patch
# User Laman
# Date 2024-06-16 16:04:44
# Node ID c827cb147cf5d073f50ad8ac88d8aa6d8f7d3eff
# Parent  a86ff65ec3210aaea7ba84221872d0f705778249

added the finite automaton determinization

diff --git a/regexp.py b/regexp.py
--- a/regexp.py
+++ b/regexp.py
@@ -141,8 +141,8 @@ def parse(pattern, offset=0):
 
 
 class Regexp:
-	def __init__(self, s):
-		(self.rules, self.end_states) = self._parse(s)
+	def __init__(self, pattern):
+		(self.rules, self.end_states) = self._parse(pattern)
 
 	def _parse(self, s):
 		r = parse(s)
@@ -181,12 +181,56 @@ class Regexp:
 
 		return any(st in self.end_states for st in current)
 
+	def determinize(self):
+		rules = dict()
+		end_states = {(-1,)} if -1 in self.end_states else set()
+
+		stack = [(-1,)]
+		processed_states = set()
+		while stack:
+			multistate = stack.pop()
+			new_rules = dict()
+			
+			for ((st, c), target) in filter(lambda item: item[0][0] in multistate, self.rules.items()):
+				if c not in new_rules:
+					new_rules[c] = set()
+				new_rules[c].update(target)
+			
+			for (c, target_set) in new_rules.items():
+				new_target = tuple(sorted(target_set))
+				rules[(multistate, c)] = new_target
+				if any(st in self.end_states for st in new_target):
+					end_states.add(new_target)
+				if new_target not in processed_states:
+					stack.append(new_target)
+					processed_states.add(new_target)
+		
+		return (rules, end_states)
+
+
+class RegexpDFA:
+	def __init__(self, pattern):
+		r = Regexp(pattern)
+		(self.rules, self.end_states) = r.determinize()
+
+	def match(self, s):
+		st = (-1,)
+
+		for c in s:
+			key = (st, c)
+			if key in self.rules:
+				st = self.rules[key]
+			else:
+				return False
+
+		return st in self.end_states
+
 
 if __name__ == "__main__":
 	tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"]
 	for pattern in ["a*b*", "a+b+", "(ab)*", "(ab)+", "a((bc)*d)*"]:
 		print("#", pattern)
-		r = Regexp(pattern)
+		r = RegexpDFA(pattern)
 		for t in tests:
 			print(t, r.match(t))
 		print()
diff --git a/src/main.rs b/src/main.rs
--- a/src/main.rs
+++ b/src/main.rs
@@ -181,6 +181,29 @@ fn parse(pattern: &String, offset: usize
 	return Chain{content: res};
 }
 
+fn encode_set(set: &HashSet<usize>) -> u64 {
+	let mut res = 0;
+	for x in set.iter() {
+		res ^= 1<<x;
+	}
+	return res;
+}
+
+fn decode_set(x: u64) ->HashSet<usize> {
+	if x == START as u64 {return HashSet::from([START]);}
+
+	let mut x = x;
+	let mut res: HashSet<usize> = HashSet::new();
+	
+	while x > 0 {
+		let y = x.trailing_zeros();
+		res.insert(y as usize);
+		x ^= 1 << y;
+	}
+
+	return res;
+}
+
 struct Regexp {
 	rules: HashMap<(usize, char), HashSet<usize>>,
 	end_states: HashSet<usize>
@@ -236,13 +259,72 @@ impl Regexp {
 
 		return multistate.iter().any(|x| self.end_states.contains(x));
 	}
+
+	fn determinize(&self) -> RegexpDFA {
+		let mut rules: HashMap<(u64, char), u64> = HashMap::new();
+		let mut end_states: HashSet<u64> = HashSet::new();
+		if self.end_states.contains(&START) {end_states.insert(START as u64);}
+
+		let mut stack = Vec::from([START as u64]);
+		let mut processed_states = HashSet::new();
+		while !stack.is_empty() {
+			let state = stack.pop().unwrap();
+			let multistate = decode_set(state);
+			let mut new_rules: HashMap<char, HashSet<usize>> = HashMap::new();
+
+			for key in self.rules.keys().filter(|key| multistate.contains(&key.0)) {
+				let (_st, c) = key;
+				if !new_rules.contains_key(c) {
+					new_rules.insert(*c, HashSet::new());
+				}
+				for target in &self.rules[key] {
+					new_rules.get_mut(c).unwrap().insert(*target);
+				}
+			}
+
+			for (c, target_set) in new_rules.into_iter() {
+				let encoded_target = encode_set(&target_set);
+				rules.insert((state, c), encoded_target);
+				if target_set.iter().any(|st| self.end_states.contains(st)) {
+					end_states.insert(encoded_target);
+				}
+				if !processed_states.contains(&encoded_target) {
+					stack.push(encoded_target);
+					processed_states.insert(encoded_target);
+				}
+			}
+		}
+
+		return RegexpDFA{rules, end_states};
+	}
+}
+
+struct RegexpDFA {
+	rules: HashMap<(u64, char), u64>,
+	end_states: HashSet<u64>
+}
+
+impl RegexpDFA {
+	fn eval(&self, s: String) -> bool {
+		let mut state = START as u64;
+
+		for c in s.chars() {
+			if let Some(x) = self.rules.get(&(state, c)) {
+				state = *x;
+			} else {
+				return false;
+			}
+		}
+
+		return self.end_states.contains(&state);
+	}
 }
 
 fn main() {
 	let tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"];
 	for pattern in ["a*b*", "a+b+", "(ab)*", "(ab)+", "a((bc)*d)*"] {
 		println!("# {pattern}");
-		let r = Regexp::new(&pattern.to_string());
+		let r = Regexp::new(&pattern.to_string()).determinize();
 		for &t in tests.iter() {
 			println!("{t} {}", r.eval(t.to_string()));
 		}