```/*
*
*  This file is the solution to an exercise problem posed during
*  one of the UW CSE 333 lectures (333exercises).
*
*  333exercises is free software: you can redistribute it and/or modify
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  333exercises is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with 333exercises.  If not, see <http://www.gnu.org/licenses/>.
*/

// Lecture 15 exercise 1

#include <cmath>

#include "./Shape.h"

#ifndef _LEC15_EX1_TRIANGLE_H_
#define _LEC15_EX1_TRIANGLE_H_

// A "Triangle" is a concrete derived class of Shape representing a
// triangle.
class Triangle : Shape {
friend class Square;
public:
Triangle(std::pair<double, double> v1,
std::pair<double, double> v2,
std::pair<double, double> v3) : v1_(v1), v2_(v2), v3_(v3) { }

~Triangle() { }

// Return the centroid of the shape.
virtual std::pair<double, double> Centroid() const;

// Return the area of the shape.
virtual double Area() const;

// Move the shape by adding "delta" to the shape.
virtual void Move(const std::pair<double, double> &delta);

// Return a string with some pretty-printed shape details.
virtual std::string Print() const;

private:
std::pair<double, double> v1_, v2_, v3_;
};

#endif  // _LEC15_EX1_TRIANGLE_H_
```