java实现八皇后问题(递归和循环两种方式)

循环方式：

package EightQueens;

 

public class EightQueensNotRecursive {

private static final boolean AVAILABLE = true;

private int squares = 8, norm = squares - 1;

private int positionInRow[] = new int[squares];

private int p=-1;

private boolean[] rows = new boolean[squares];

private boolean[] column = new boolean[squares];

private boolean[] leftDiagonal = new boolean[2 * squares - 1];

private boolean[] rightDiagonal = new boolean[2 * squares - 1];

private static int howMany = 0;

 

public EightQueensNotRecursive() {

// To complete the initialization work for the

// column,leftDiagonal,rigthDiagonal.

for (int i = 0; i < squares; i++) {

rows[i] = AVAILABLE;

column[i] = AVAILABLE;

positionInRow[i] = -1;

}

for (int i = 0; i < 2 * squares - 1; i++) {

leftDiagonal[i] = AVAILABLE;

rightDiagonal[i] = AVAILABLE;

}

 

}

 

public void printResults(int[] columns) {

int row, col;

System.out.println("八皇后问题的第 " + howMany + " 种解法");

System.out.print("八皇后问题的结果为：");

for (int e : columns) {

System.out.print(e);

}

System.out.println("\n具体的图示如下图所示：");

for (row = 0; row < squares; row++) {

for (col = 0; col < squares; col++) {

if (col == positionInRow[row]) {

System.out.print("@");

} else {

System.out.print("*");

}

}

System.out.println();

}

System.out.println();

}

 

public void putQueen() 

{

int row=0, col;

while (true) 

{

for (col = p + 1; col < squares; col++)

{

if(rows[row]==AVAILABLE&&column[col]==AVAILABLE&&leftDiagonal[row+col]==AVAILABLE&&rightDiagonal[row-col+norm]==AVAILABLE)

{

break;

}

}

//在当前的行里面找到了可以放置皇后的位置

if(col<squares)

{

rows[row]=!AVAILABLE;

column[col]=!AVAILABLE;

leftDiagonal[row+col]=!AVAILABLE;

rightDiagonal[row-col+norm]=!AVAILABLE;

positionInRow[row]=col;

p=col;

}else//如果当前行没办反放置皇后了，那么回溯

{

if(row>0)//到前一行

{

row--;

p=positionInRow[row];

rows[row]=AVAILABLE;

column[p]=AVAILABLE;

leftDiagonal[row+p]=AVAILABLE;

rightDiagonal[row-p+norm]=AVAILABLE;

positionInRow[row]=-1;

continue;

}else

{

break;

}

}

if(row==squares-1)

{

howMany+=1;

printResults(positionInRow);

p=positionInRow[row];

rows[row]=AVAILABLE;

column[p]=AVAILABLE;

leftDiagonal[row+p]=AVAILABLE;

rightDiagonal[row-p+norm]=AVAILABLE;

positionInRow[row]=-1;

continue;

}

else

{

row++;

p=-1;

continue;

}

}

}

public static void main(String args[])

{

EightQueensNotRecursive eightQueens=new EightQueensNotRecursive();

eightQueens.putQueen();

System.out.println("皇后问题一共有"+howMany+"种解法");

}

 

}

 

递归方式：

package EightQueens;

 

public class EightQueensRecursive {

private static final boolean AVAILABLE=true;

private int squares=8,norm=squares-1;

private int positionInRow[]=new int[squares];

private boolean[] column=new boolean[squares];

private boolean[] leftDiagonal=new boolean[2*squares-1];

private boolean[] rightDiagonal=new boolean[2*squares-1];

private static int howMany=0;

public EightQueensRecursive(){

//To complete the initialization work for the column,leftDiagonal,rigthDiagonal.

for(int i=0;i<squares;i++){

column[i]=AVAILABLE;

positionInRow[i]=-1;

}

for(int i=0;i<2*squares-1;i++){

leftDiagonal[i]=AVAILABLE;

rightDiagonal[i]=AVAILABLE;

}

}

public void printResults(int[] columns){

int row,col;

System.out.println("八皇后问题的第 "+howMany+" 种解法");

System.out.print("八皇后问题的结果为：");

for(int e:columns){

System.out.print(e);

}

System.out.println("\n具体的图示如下图所示：");

for(row=0;row<squares;row++){

for(col=0;col<squares;col++){

if(col==positionInRow[row]){

System.out.print("@");

}else{

System.out.print("*");

}

}

System.out.println();

}

System.out.println();

}

public void putQueen(int row){

//如果前面已经得到了一个可行解

for(int i=0;i<squares;i++)

{

if(row>squares-1) break;

if(column[i]==AVAILABLE&&leftDiagonal[row+i]==AVAILABLE&&rightDiagonal[row-i+norm]==AVAILABLE)

{

positionInRow[row]=i;

column[i]=!AVAILABLE;

leftDiagonal[row+i]=!AVAILABLE;

rightDiagonal[row-i+norm]=!AVAILABLE;

if(row<squares-1){

putQueen(row+1);

}else

{

howMany+=1;

printResults(positionInRow);

}

column[i]=AVAILABLE;

leftDiagonal[row+i]=AVAILABLE;

rightDiagonal[row-i+norm]=AVAILABLE;

}

}

}

public static void main(String args[]){

EightQueensRecursive eightQueens=new EightQueensRecursive();

eightQueens.putQueen(0);

System.out.println("皇后问题一共找到了 "+howMany+"组解。");

}

}