nfa确定化java实现

以下是一个简单的NFA确定化Java实现：

import java.util.*;

public class NFA {

    private int numStates;
    private Set<Integer> acceptStates;
    private Map<Integer, Map<Character, Set<Integer>>> transitionTable;

    public NFA(int numStates) {
        this.numStates = numStates;
        this.acceptStates = new HashSet<>();
        this.transitionTable = new HashMap<>();
    }

    public void addTransition(int state, char symbol, int nextState) {
        Map<Character, Set<Integer>> transitions = transitionTable.getOrDefault(state, new HashMap<>());
        Set<Integer> nextStates = transitions.getOrDefault(symbol, new HashSet<>());
        nextStates.add(nextState);
        transitions.put(symbol, nextStates);
        transitionTable.put(state, transitions);
    }

    public void addAcceptState(int state) {
        acceptStates.add(state);
    }

    public DFA toDFA() {
        Map<Set<Integer>, Integer> stateMap = new HashMap<>();
        int nextState = 0;
        Set<Integer> startState = epsilonClosure(Collections.singleton(0));
        stateMap.put(startState, nextState);
        nextState++;

        Map<Integer, Map<Character, Integer>> dfaTransitionTable = new HashMap<>();
        Set<Set<Integer>> unmarkedStates = new HashSet<>();
        unmarkedStates.add(startState);

        while (!unmarkedStates.isEmpty()) {
            Set<Integer> currentDfaState = unmarkedStates.iterator().next();
            unmarkedStates.remove(currentDfaState);

            for (char symbol : getAlphabet()) {
                Set<Integer> nextNfaState = new HashSet<>();
                for (int state : currentDfaState) {
                    Map<Character, Set<Integer>> transitions = transitionTable.getOrDefault(state, new HashMap<>());
                    Set<Integer> nextStates = transitions.getOrDefault(symbol, Collections.emptySet());
                    nextNfaState.addAll(epsilonClosure(nextStates));
                }

                if (!nextNfaState.isEmpty()) {
                    if (!stateMap.containsKey(nextNfaState)) {
                        stateMap.put(nextNfaState, nextState);
                        nextState++;
                        unmarkedStates.add(nextNfaState);
                    }
                    int dfaNextState = stateMap.get(nextNfaState);
                    Map<Character, Integer> transitions = dfaTransitionTable.getOrDefault(stateMap.get(currentDfaState), new HashMap<>());
                    transitions.put(symbol, dfaNextState);
                    dfaTransitionTable.put(stateMap.get(currentDfaState), transitions);
                }
            }
        }

        Set<Integer> dfaAcceptStates = new HashSet<>();
        for (Set<Integer> nfaAcceptState : acceptStates) {
            if (stateMap.containsKey(nfaAcceptState)) {
                dfaAcceptStates.add(stateMap.get(nfaAcceptState));
            }
        }

        return new DFA(nextState, dfaAcceptStates, dfaTransitionTable);
    }

    private Set<Integer> epsilonClosure(Set<Integer> states) {
        Set<Integer> closure = new HashSet<>(states);
        Stack<Integer> stack = new Stack<>();
        stack.addAll(states);

        while (!stack.isEmpty()) {
            int state = stack.pop();
            Map<Character, Set<Integer>> transitions = transitionTable.getOrDefault(state, new HashMap<>());
            Set<Integer> epsilonStates = transitions.getOrDefault(null, Collections.emptySet());
            for (int epsilonState : epsilonStates) {
                if (!closure.contains(epsilonState)) {
                    closure.add(epsilonState);
                    stack.push(epsilonState);
                }
            }
        }

        return closure;
    }

    private Set<Character> getAlphabet() {
        Set<Character> alphabet = new HashSet<>();
        for (Map<Character, Set<Integer>> transitions : transitionTable.values()) {
            alphabet.addAll(transitions.keySet());
        }
        alphabet.remove(null);
        return alphabet;
    }
}

该类包含一个NFA的转换表和接受状态集合。它还包含一个方法，将NFA转换为DFA。在toDFA方法中，我们使用epsilon闭包算法来计算NFA的状态集合。然后，我们使用一个哈希表来将NFA状态集合映射到DFA状态。我们遍历DFA状态并为每个符号计算转换，然后将结果添加到DFA转换表中。最后，我们从NFA接受状态集合中计算DFA接受状态集合。

此实现有待改进，例如需要考虑带有ε转换的NFA，并且可以使用更高效的数据结构来表示状态和转换。