c++求first和follow集代码

以下是C++代码实现First和Follow集合的算法：

First集合算法：

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>

using namespace std;

map<string, set<string>> first;

void compute_first(string non_terminal, vector<vector<string>> productions) {
    for (auto production : productions) {
        if (production[0] == non_terminal) {
            if (production[1] == "epsilon") {
                first[non_terminal].insert("epsilon");
            } else if (islower(production[1][0])) {
                first[non_terminal].insert(production[1]);
            } else {
                compute_first(production[1], productions);
                for (auto element : first[production[1]]) {
                    first[non_terminal].insert(element);
                }
            }
        }
    }
}

int main() {
    vector<vector<string>> productions = {
        {"S", "AB"},
        {"A", "aA"},
        {"A", "epsilon"},
        {"B", "bB"},
        {"B", "epsilon"}
    };

    for (auto production : productions) {
        compute_first(production[0], productions);
    }

    for (auto element : first) {
        cout << "First(" << element.first << ") = { ";
        for (auto value : element.second) {
            cout << value << " ";
        }
        cout << "}" << endl;
    }

    return 0;
}

Follow集合算法：

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>

using namespace std;

map<string, set<string>> follow;

void compute_follow(string non_terminal, vector<vector<string>> productions) {
    if (non_terminal == productions[0][0]) {
        follow[non_terminal].insert("$");
    }

    for (auto production : productions) {
        for (int i = 1; i < production.size(); i++) {
            if (production[i] == non_terminal) {
                if (i == production.size() - 1) {
                    compute_follow(production[0], productions);
                    for (auto element : follow[production[0]]) {
                        follow[non_terminal].insert(element);
                    }
                } else {
                    if (islower(production[i + 1][0])) {
                        follow[non_terminal].insert(production[i + 1]);
                    } else {
                        compute_first(production[i + 1], productions);
                        for (auto element : first[production[i + 1]]) {
                            if (element != "epsilon") {
                                follow[non_terminal].insert(element);
                            } else {
                                compute_follow(production[0], productions);
                                for (auto element : follow[production[0]]) {
                                    follow[non_terminal].insert(element);
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

int main() {
    vector<vector<string>> productions = {
        {"S", "AB"},
        {"A", "aA"},
        {"A", "epsilon"},
        {"B", "bB"},
        {"B", "epsilon"}
    };

    for (auto production : productions) {
        compute_follow(production[0], productions);
    }

    for (auto element : follow) {
        cout << "Follow(" << element.first << ") = { ";
        for (auto value : element.second) {
            cout << value << " ";
        }
        cout << "}" << endl;
    }

    return 0;
}