Lambda Equation Eval

lambdaEval.cpp

#include <bits/stdc++.h>
using namespace std;

/*
 @author: wilson
 */

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    string s;
    getline(cin, s);

    int n = (int) s.length();

    map<string, int> mp;

    vector<string> st;

    set<string> free_vars;

    for (int i = 0; i < n; i++) {
        if (s[i] == ')') {
            while (st.back() != "(") {
                string cur = st.back();
                --mp[cur];
                if (mp[cur] == 0)
                    mp.erase(cur);
                st.pop_back();
            }
            string cur = st.back();

            --mp[cur];
            if (mp[cur] == 0)
                mp.erase(cur);
            st.pop_back();
            continue;
        }
        if (s[i] == ' ' || s[i] == '.') continue;
        if (i + 2 < n && s.substr(i, 2) == "λ") {
            ++mp[s.substr(i, 3)];
            st.emplace_back(s.substr(i, 3));
            i += 2;
        } else {
            string cur = s.substr(i, 1);
            st.emplace_back(cur);
            ++mp[cur];
            if (cur != "(" && !cur.empty()) {
                string tmp = cur;
                cur = "λ" + cur;
                if (!mp.count(cur)) {
                    free_vars.emplace(tmp);
                }
            }
        }
    }

    if (free_vars.empty()) {
        cout << "closed term" << endl;
    } else {
        vector<string> free_vals(begin(free_vars), end(free_vars));
        int m = int(free_vals.size());
        for (int i = 0; i < m; i++) {
            cout << free_vals[i];
            if (i != m - 1)
                cout << ", ";
        }
        cout << endl;
    }

    return 0;
}