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use crate::regex::Regex;
use std::{collections::HashMap, str::Chars, usize};
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Trans {
Symbol(char),
Epsilon,
}
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct State {
id: usize,
transitions: Vec<(usize, Trans)>,
}
impl State {
fn new(id: usize) -> Self {
Self {
id,
transitions: Vec::new(),
}
}
}
#[derive(Debug, Clone, PartialEq)]
pub struct NFA {
pub states: HashMap<usize, State>,
transitions: HashMap<usize, Vec<usize>>,
initial_state: usize,
accepting_states: Vec<usize>,
}
impl From<Regex> for NFA {
fn from(regex: Regex) -> Self {
let mut nfa = NFA::new();
nfa.regex_to_nfa(regex);
nfa
}
}
impl NFA {
pub fn new() -> Self {
Self {
states: HashMap::new(),
transitions: HashMap::new(),
initial_state: 0,
accepting_states: Vec::new(),
}
}
pub fn add_state(&mut self) -> usize {
let new_state = State::new(self.states.len());
let id = new_state.id;
self.states.insert(id, new_state);
id
}
pub fn regex_to_nfa_helper(&mut self, regex: Regex) -> (usize, usize) {
match regex {
Regex::Symbol(ch) => {
let first = self.add_state();
let last = self.add_state();
self.add_transition(first, last, Trans::Symbol(ch));
(first, last)
}
Regex::Concat((left, right)) => {
let first = self.add_state();
let (l_first, l_last) = self.regex_to_nfa_helper(*left);
let (r_first, r_last) = self.regex_to_nfa_helper(*right);
self.add_transition(first, l_first, Trans::Epsilon);
self.add_transition(l_last, r_first, Trans::Epsilon);
(first, r_last)
}
Regex::Union((left, right)) => {
let first = self.add_state();
let (l_first, l_last) = self.regex_to_nfa_helper(*left);
let (r_first, r_last) = self.regex_to_nfa_helper(*right);
self.add_transition(first, l_first, Trans::Epsilon);
self.add_transition(first, r_first, Trans::Epsilon);
let last = self.add_state();
self.add_transition(l_last, last, Trans::Epsilon);
self.add_transition(r_last, last, Trans::Epsilon);
(first, last)
}
Regex::Plus(_) => todo!(),
Regex::Star(tok) => {
let first = self.add_state();
let (t_first, t_last) = self.regex_to_nfa_helper(*tok);
self.add_transition(first, t_first, Trans::Epsilon);
self.add_transition(t_last, first, Trans::Epsilon);
let last = self.add_state();
self.add_transition(first, last, Trans::Epsilon);
self.add_transition(t_last, last, Trans::Epsilon);
(first, last)
}
Regex::Dot => {
let first = self.add_state();
(first, first)
}
Regex::None => {
let state = self.add_state();
(state, state)
}
}
}
pub fn regex_to_nfa(&mut self, regex: Regex) {
let (_, last) = self.regex_to_nfa_helper(regex);
self.accepting_states.push(last);
}
pub fn add_transition(&mut self, from: usize, to: usize, trans: Trans) {
self.transitions
.entry(from)
.and_modify(|val| val.push(to))
.or_insert_with(|| vec![to]);
self.states
.get_mut(&from)
.unwrap()
.transitions
.push((to, trans));
}
fn matches_helper(&self, state: &State, mut chars: Chars) -> bool {
println!("{state:?}\n{chars:?}");
if self.accepting_states.contains(&state.id) {
return chars.next().is_none();
}
let mut result = false;
for (id, trans) in &state.transitions {
match trans {
Trans::Symbol(ch) => {
if *id == state.id {
chars.next();
result |= self.matches_helper(self.states.get(id).unwrap(), chars.clone());
}
let mut cloned = chars.clone().peekable();
let nxt_peek = cloned.peek();
match nxt_peek {
Some(nxt) if nxt == ch => {
chars.next();
result |=
self.matches_helper(self.states.get(id).unwrap(), chars.clone());
}
None => {}
_ => {}
}
}
Trans::Epsilon => {
result |= self.matches_helper(self.states.get(id).unwrap(), chars.clone());
}
}
}
result
}
pub fn matches(&self, input: &str) -> bool {
let chars = input.chars();
self.matches_helper(self.states.get(&self.initial_state).unwrap(), chars)
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::regex::Regex;
fn test(regex: &str, input: &str) -> bool {
let token = Regex::new(regex);
let mut nfa = NFA::new();
nfa.regex_to_nfa(token);
let mut x: Vec<(&usize, &State)> = nfa.states.iter().map(|(k, v)| (k, v)).collect();
x.sort();
nfa.matches(input)
}
#[test]
fn test_concat_succ() {
assert!(test("abc", "abc"));
assert!(test("", ""));
assert!(test("Thisshouldmatch", "Thisshouldmatch"));
}
#[test]
fn test_concat_fail() {
assert!(!test("abc", "abd"));
assert!(!test("abc", "abd"));
assert!(!test("abc", "abcc"));
assert!(!test("abc", "notabc"));
assert!(!test("abc", ""));
}
#[test]
fn test_union_succ() {
assert!(test("(a|b)", "a"));
assert!(test("(a|b|c|d)", "a"));
assert!(test("(a|b|c|d)", "b"));
assert!(test("(a|b|c|d)", "d"));
assert!(test("(a|b|c|d)", "c"));
assert!(test("(a|b)", "b"));
assert!(test("(a|b)b", "bb"));
assert!(test("(a|b)a", "ba"));
}
#[test]
fn test_union_fail() {
assert!(!test("(a|b)", "x"));
assert!(!test("(a|b)", "ax"));
}
#[test]
fn test_star_succ() {
assert!(test("(0)*1(0)*", "000000000100000"));
assert!(test("(a)*abc(a)*", "aaaaaaabcaaaaaa"));
assert!(test("a*b", "b"));
assert!(test("a*bcd", "aaaaaabcd"));
}
#[test]
fn test_star_fail() {
assert!(!test("a*b", "aabbbb"));
assert!(!test("1*0", "20"));
assert!(!test("(0)*1(0)*", "101100000"));
}
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