Leetcode 10 NFA

struct State;
typedef pair<char, State*> edge;
struct State {
    bool fin;
    vector<edge> edges;
    
    State() {
        fin = false;
    }
};

State *constructNFA(string p) {
    if (p.size() == 0) return NULL;
    if (p.size() == 1 && p[0] == '*') return NULL;
    
    State *init = new State();
    State *curr = init;
    
    unsigned int i = 0;
    while (i < p.size()) {
        if (p[i] == '*') {
            i++; continue;
        } else {
            if (p[i+1] == '*') {
                curr->edges.push_back({p[i], curr});
                State *s = new State();
                curr->edges.push_back({'@', s});
                curr = s;
                i += 2;
            } else {
                State *s = new State();
                curr->edges.push_back({p[i], s});
                curr = s;
                i++;
            }
        }
    }
    curr -> fin = true;
    return init;
}

void epsilonTransition(vector<State *> &states) {
    unsigned int i = 0;
    while (i < states.size()) {
        for (edge e: states[i]->edges) {
            if (e.first == '@') {
                auto it = find(states.begin(), states.end(), e.second);
                if (it == states.end())
                    states.push_back(e.second);
            }
        }
        i++;
    }
    return;
}

class Solution {
public:
    bool isMatch(string s, string p) {
        if (s.size() == 0 && p.size() == 0) return true;
        State *nfa = constructNFA(p);
        if (!nfa) return false;
        vector<State *> states = {nfa};
        epsilonTransition(states);
        for (char &c : s) {
            vector<State *> next;
            for (State *node : states) {
                for (edge e : node->edges) {
                    if (e.first == '.') {
                        next.push_back(e.second);
                    }
                    if (e.first == c) {
                        next.push_back(e.second);
                    }
                }
            }
            epsilonTransition(next);
            states = next;
        }
        for (State *node : states) {
            if (node -> fin)
                return true;
        }
        return false;
    }
};