From 4dc4eff5a38bf00d7cda9fd2d79589f95c86a0f7 Mon Sep 17 00:00:00 2001
From: agicy <2359800311@qq.com>
Date: Wed, 27 Mar 2024 23:37:43 +0800
Subject: [PATCH] feat: implement DFA minimization

- Developed an algorithm to minimize a Deterministic Finite Automaton (DFA) by merging equivalent states.
- Ensured the algorithm efficiently reduces the number of states while preserving the language recognized by the DFA.
- Validated the correctness of the minimization process through comprehensive unit tests.
---
 src/algorithms/minimize_dfa.py | 42 +++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/algorithms/minimize_dfa.py b/src/algorithms/minimize_dfa.py
index 4fc91f3..66b756b 100644
--- a/src/algorithms/minimize_dfa.py
+++ b/src/algorithms/minimize_dfa.py
@@ -3,5 +3,45 @@
 __all__: list[str] = ["minimize_dfa"]
 
 
+def _hopcroft(dfa: DFA) -> list[set[str]]:
+    P: list[set[str]] = [dfa.qf, dfa.Q - dfa.qf]
+    W: list[set[str]] = [dfa.qf]
+    while W:
+        A: set[str] = W.pop()
+        for c in dfa.T:
+            X = set(q for q in dfa.Q if (q, c) in dfa.delta and dfa.delta[(q, c)] in A)
+            for Y in P[:]:
+                if X & Y and (Y - X) & Y:
+                    P.remove(Y)
+                    P.append(X & Y)
+                    P.append((Y - X) & Y)
+                    if Y in W:
+                        W.remove(Y)
+                        W.append(X & Y)
+                        W.append((Y - X) & Y)
+                    else:
+                        if len(X & Y) <= len((Y - X) & Y):
+                            W.append(X & Y)
+                        else:
+                            W.append((Y - X) & Y)
+    return P
+
+
 def minimize_dfa(dfa: DFA) -> DFA:
-    pass
+    partition: list[set[str]] = _hopcroft(dfa=dfa)
+    partition.reverse()
+    dic: dict[str, str] = {
+        state: f"q{i}"
+        for i, subset in enumerate(iterable=partition)
+        for state in subset
+    }
+    Q: set[str] = set(dic.values())
+    T: set[str] = dfa.T
+    delta: dict[tuple[str, str], str] = {
+        (dic[state], symbol): dic[dfa.delta[(state, symbol)]]
+        for state in dfa.Q
+        for symbol in dfa.T
+    }
+    q0: str = dic[dfa.q0]
+    qf: set[str] = {dic[state] for state in dfa.qf}
+    return DFA(Q=Q, T=T, delta=delta, q0=q0, qf=qf)