#include <iostream>
using namespace std;
 
class StrategyInterface
{
public:
    virtual void execute() const = 0;
};
 
class ConcreteStrategyA: public StrategyInterface
{
public:
    virtual void execute() const
    {
        cout << "Called ConcreteStrategyA execute method" << endl;
    }
};
 
class ConcreteStrategyB: public StrategyInterface
{
public:
    virtual void execute() const
    {
        cout << "Called ConcreteStrategyB execute method" << endl;
    }
};
 
class ConcreteStrategyC: public StrategyInterface
{
public:
    virtual void execute() const
    {
        cout << "Called ConcreteStrategyC execute method" << endl;
    }
};
 
class Context
{
private:
    StrategyInterface * strategy_;
 
public:
    explicit Context(StrategyInterface *strategy):strategy_(strategy)
    {
    }
 
    void set_strategy(StrategyInterface *strategy)
    {
        strategy_ = strategy;
    }
 
    void execute() const
    {
        strategy_->execute();
    }
};
 
int main(int argc, char *argv[])
{
    ConcreteStrategyA concreteStrategyA;
    ConcreteStrategyB concreteStrategyB;
    ConcreteStrategyC concreteStrategyC;
 
    Context contextA(&concreteStrategyA);
    Context contextB(&concreteStrategyB);
    Context contextC(&concreteStrategyC);
 
    contextA.execute(); // output: "Called ConcreteStrategyA execute method"
    contextB.execute(); // output: "Called ConcreteStrategyB execute method"
    contextC.execute(); // output: "Called ConcreteStrategyC execute method"
 
    contextA.set_strategy(&concreteStrategyB);
    contextA.execute(); // output: "Called ConcreteStrategyB execute method"
    contextA.set_strategy(&concreteStrategyC);
    contextA.execute(); // output: "Called ConcreteStrategyC execute method"
 
    return 0;
}