YB5.11 Описание и обзор общего решения задачи

RobertDeMilo

Apr 15th, 2024

Never

Add comment

Not a member of Pastebin yet? Sign Up, it unlocks many cool features!

C++ 3.12 KB | None | 0 0

raw download clone embed print report

#include <iostream>
#include <string>
#include <memory>
#include <stack>
using namespace std;
class Node
{
public:
virtual int Evaluate() const = 0;
};
class Value : public Node
{
public:
Value(char digit) : _value(digit - '0') {}
int Evaluate() const override { return _value; }
private:
const int _value;
};
class Variable : public Node
{
public:
Variable(const int& x) : _x(x) {}
int Evaluate() const override { return _x; }
private:
const int& _x;
};
class Operation : public Node
{
public:
Operation(char value) : precedence([value] {
if (value == '+')
{
return 2;
}
else
{
return 1;
}
}()), _op(value) {}
const int precedence;
int Evaluate() const override
{
if (_op == '*')
{
return _left->Evaluate() * _right->Evaluate();
}
else if (_op == '+')
{
return _left->Evaluate() + _right->Evaluate();
}
else if (_op == '-')
{
return _left->Evaluate() - _right->Evaluate();
}
return 0;
}
void SetLeft(shared_ptr<Node> node)
{
_left = node;
}
void SetRight(shared_ptr<Node> node)
{
_right = node;
}
private:
const char _op;
shared_ptr<Node> _left, _right;
};
template <class Iterator>
shared_ptr<Node> Parse(Iterator token, Iterator end, const int& x)
{
if (token == end)
{
return make_shared<Value>('0');
}
stack<shared_ptr<Node>> values;
stack<shared_ptr<Operation>> ops;
auto PopOps = [&](int precedence) {
while (!ops.empty() && ops.top()->precedence >= precedence)
{
auto value1 = values.top();
values.pop();
auto value2 = values.top();
values.pop();
auto op = ops.top();
ops.pop();
op->SetRight(value1);
op->SetLeft(value2);
values.push(op);
}
};
while (token != end)
{
const auto& value = *token;
if (value >= '0' && value <= '9')
{
values.push(make_shared<Value>(value));
}
else if (value == 'x')
{
values.push(make_shared<Variable>(x));
}
else if (value == '*')
{
PopOps(2);
ops.push(make_shared<Operation>(value));
}
else if (value == '+' || value == '-')
{
PopOps(1);
ops.push(make_shared<Operation>(value));
}
++token;
}
while (!ops.empty())
{
PopOps(0);
}
return values.top();
}
int main()
{
string tokens;
cout << "Enter expression: ";
getline(cin, tokens);
int x = 0;
auto node = Parse(tokens.begin(), tokens.end(), x);
cout << "Enter x: ";
while (cin >> x)
{
cout << "Expression value: " << node->Evaluate() << endl;
cout << "Enter x: ";
}
return 0;
}

Add Comment

Please, Sign In to add comment