eight queen.cpp

这是用类的方法解决八皇后问题

# include <iostream>
using namespace std;
# define bool int // not all compilers yet support booleans

class queen {
public:
		// constructor
	queen (int, queen *);
	
		// find and print solutions
	bool findSolution();
	bool advance();
	void print();

private:
		// data fields
	int row;
	const int column;
	queen * neighbor;
	
		// internal method
	bool canAttack (int, int);
};

queen::queen(int col, queen * ngh)
	: column(col), neighbor(ngh)
{
	row = 1;
}

bool queen::canAttack (int testRow, int testColumn)
{
		// test rows
	if (row == testRow)
		return true;
		
		// test diagonals
	int columnDifference = testColumn - column;
	if ((row + columnDifference == testRow) ||
		(row - columnDifference == testRow))
			return true;
			
		// try neighbor
	return neighbor && neighbor->canAttack(testRow, testColumn);
}

bool queen::findSolution()
{
	// test position against neighbors

        // The while loop is not necessary since advance() always
        // moves the queen to the next "safe" position.
        // [Jerry Roth, Gonzaga University, Feb. 2000]

	//while (neighbor && neighbor->canAttack (row, column)) 
	if (neighbor && neighbor->canAttack (row, column)) 
		if (! advance())
			return false;
			
			// found a solution
	return true;
}

bool queen::advance()
{
	if (row < 8) {
		row++;
		return findSolution();
		}
		
//	if (neighbor && ! neighbor->advance())
//		return false;
// The above test does not return false when queen 1 runs out of rows.
// We alter the test to return false if we do not have a neighbor, or
// if our neighbor cannot advance.
// [Jerry Roth, Gonzaga University, Feb. 2000]
	if (! neighbor || ! neighbor->advance())
		return false;

	row = 1;
	return findSolution();
}

void queen::print()
{
	if (neighbor)
		neighbor->print();
	cout << "column " << column << " row " << row << '\n';
}

int main() {
	int count = 1;
	queen * lastQueen = 0;
	
	for (int i = 1; i <= 8; i++) {
		lastQueen = new queen(i, lastQueen);
		if (! lastQueen->findSolution())
			cout << "no solution\n";
		}
	cout << "\n\nSolution " << count++ << " ==============" << endl;
	lastQueen->print();

	while (lastQueen->advance()) {
	  cout << "\n\nSolution " << count++ << " ==============" << endl;
	  lastQueen->print();
	}
	
	system("pause");
	return 0;
}