幻方笔试题-语言解释器

幻方笔试题-语言解释器.cpp

#include <bits/stdc++.h>
#define ll long long

using namespace std;

bool isEmpty(char c)
{
  return c == ' ' or c == '\n' or c == '\t';
}
string inv(string c)
{
  if (c == "0")
  {
    return c;
  }
  if (c[0] == '-')
  {
    return c.substr(1);
  }
  return "-" + c;
}

string sub(string, string);
string add(string a, string b)
{
  if (a[0] == '-' and b[0] == '-')
  {
    return inv(add(a.substr(1), b.substr(1)));
  }
  else if (a[0] == '-')
  {
    return sub(b, a.substr(1));
  }
  else if (b[0] == '-')
  {
    return sub(a, b.substr(1));
  }
  int la = a.size();
  int lb = b.size();
  int c = 0;
  string temp;
  for (int i = 1; la - i >= 0 or lb - i >= 0; i++)
  {
    int d1 = la - i >= 0 ? a[la - i] - '0' : 0;
    int d2 = lb - i >= 0 ? b[lb - i] - '0' : 0;
    int d = (d1 + d2 + c) % 10;
    c = (d1 + d2 + c) / 10;
    temp += to_string(d);
  }
  if (c)
  {
    temp += '1';
  }
  reverse(temp.begin(), temp.end());
  return temp;
}
string sub(string a, string b)
{
  if (a[0] == '-' and b[0] == '-')
  {
    return sub(b.substr(1), a.substr(1));
  }
  else if (a[0] == '-')
  {
    return inv(add(a.substr(1), b));
  }
  else if (b[0] == '-')
  {
    return add(a, b.substr(1));
  }
  int la = a.size();
  int lb = b.size();
  if (la == lb)
  {
    if (a < b)
    {
      return inv(sub(b, a));
    }
  }
  else if (la < lb)
  {
    return inv(sub(b, a));
  }
  int c = 0;
  string temp;
  for (int i = 1; la - i >= 0 or lb - i >= 0; i++)
  {
    int d1 = la - i >= 0 ? a[la - i] - '0' : 0;
    int d2 = lb - i >= 0 ? b[lb - i] - '0' : 0;
    int d = (10 + d1 - d2 + c) % 10;
    if (d1 - d2 + c >= 0)
    {
      c = 0;
    }
    else
    {
      c = -1;
    }
    temp += to_string(d);
  }
  reverse(temp.begin(), temp.end());
  for (int i = 0; i < temp.size(); i++)
  {
    if (temp[i] != '0')
    {
      return string(temp.begin() + i, temp.end());
    }
  }
  return "0";
}

class Eval
{
public:
  string s;
  int i;
  int n;
  map<string, string> m;
  Eval(string s)
  {
    n = s.size();
    this->s = s;
    i = 0;
  }
  void skip()
  {
    while (i < n and isEmpty(s[i]))
    {
      i++;
    }
  }
  string get_id()
  {
    skip();
    string temp;
    for (; i < n; i++)
    {
      if (isEmpty(s[i]))
      {
        i--;
        break;
      }
      else if (isalnum(s[i]))
      {
        temp += s[i];
      }
      else
      {
        i--;
        break;
      }
    }
    i++;
    skip();
    return temp;
  }
  string get_value()
  {
    string num = get_num();
    if (num.size())
    {
      return num;
    }
    else
    {
      string id = get_id();
      return m[id];
    }
  }
  string get_num()
  {
    string temp;
    skip();
    for (; i < n; i++)
    {
      if (isdigit(s[i]))
      {
        temp += s[i];
      }
      else
      {
        break;
      }
    }
    return temp;
  }
  void exec_statements(bool dummy = false)
  {
    while (i < n)
    {
      skip();
      if (s[i] == ';')
      {
        i++;
        continue;
      }
      if (s[i] == '{')
      {
        i++;
        exec_statements();
        continue;
      }
      if (s[i] == '}')
      {
        i++;
        return;
      }
      if (s[i] == '!')
      {
        i++;
        string v = get_value();
        if (!dummy)
        {
          cout << "output:" << v << endl;
        }
      }
      else
      {
        string id = get_id();
        string op;
        op += s[i];
        if (op == "=")
        {
          i++;
          string v = get_value();
          if (!dummy)
          {
            m[id] = v;
          }
        }
        else if (op == "+")
        {
          i++;
          i++;
          string v = get_value();
          if (!dummy)
          {
            m[id] = add(m[id], v);
          }
        }
        else if (op == "-")
        {
          i++;
          i++;
          string v = get_value();
          if (!dummy)
          {
            m[id] = sub(m[id], v);
          }
        }
        else if (s[i] == '?')
        {
          i++;
          string v = get_value();
          if (v == "0")
          {
            exec_statements();
          }
          else
          {
            exec_statements(true);
          }
        }
      }
    }
  }
};

int main()
{
#ifdef _DEBUG
  freopen("input.txt", "r", stdin);
  // freopen("output.txt", "w", stdout);
#endif
  string s = "\
      a = 0; \
  b = 100000000000000000000000000000000000000000000000000000000000000;     \
  c = 128937129371929812123789123789012367412347893;     \
  b += a;    \
  c -= b;    \
  ? a        \
  {          \
    !b;      \
    b = 0    \
  };         \
  ? b        \
  {          \
    !c;      \
    c = 0;   \
  };         \
  ? c        \
  {          \
    !a       \
  }          \
  ";
  auto e = Eval(s);
  e.exec_statements();
  return 0;
}