著名的八皇后问题

package com.zhang.csdn;import java.io.File;import java.io.FileWriter;import java.io.IOException;class EightQueen {private static int total = 0;private final static int EIGHT_QUEEN_ROW = 8;private final static int EIGHT_QUEEN_COLUMN = 8;    private final static String RESULT_FILE_DISK = "E:";private final static String RESULT_FILE_NAME = "EightQueen.txt";private final static char RESULT_OTHER_CHAR = '*';private final static char RESULT_QUEEN_CHAR = 'Q';private final static String RESULT_LINE_SEPARATOR = "\r\n";private final static String RESULT_EACH_SEPARATOR = "\r\n";private final int[] column = new int[EIGHT_QUEEN_ROW];private StringBuffer result =  new StringBuffer();public void execute() {this.initColumn();this.permute(0);this.displayResult();}private void displayResult() {        System.out.println("total : " + total);this.writeToFile(this.result);}private void initColumn() {for (int i = 0; i < EIGHT_QUEEN_ROW; i++) {column[i] = i;}}private void permute(int index) {if (index == EIGHT_QUEEN_ROW) {if (isValid()) {print();total++;}} else {for (int i = index; i < EIGHT_QUEEN_ROW; i++) {swap(i, index);permute(index + 1);swap(i, index);}}}private void print() {this.appendToResult();}private StringBuffer eachLine(int rowIndex) {  StringBuffer line = new StringBuffer(EIGHT_QUEEN_COLUMN);    for (int columnIndex = 0; columnIndex < EIGHT_QUEEN_COLUMN; columnIndex++) {        line.append( (column[rowIndex] != columnIndex ?           EightQueen.RESULT_OTHER_CHAR : EightQueen.RESULT_QUEEN_CHAR) );    }    return line.append(EightQueen.RESULT_LINE_SEPARATOR);}private void appendToResult() {  StringBuffer singleAnswer = new StringBuffer();          for (int rowIndex = 0; rowIndex < EIGHT_QUEEN_ROW; rowIndex++) {          singleAnswer.append(eachLine(rowIndex));              }          result.append(singleAnswer).append(EightQueen.RESULT_EACH_SEPARATOR);}private static void writeToFile(StringBuffer sb) {   FileWriter writer = null;         try {       File file = new File( EightQueen.RESULT_FILE_DISK +                      File.separator +                      EightQueen.RESULT_FILE_NAME);                     if (!file.exists()) {               file.createNewFile();             }             writer = new FileWriter(file);                 writer.write(sb.toString());           writer.flush();           writer.close();       } catch(Exception e) {       e.printStackTrace();       } finally {               }}private void swap(int i, int j) {int temp = column[i];column[i] = column[j];column[j] = temp;}private boolean isValid() {for (int firstLayer = 0; firstLayer < EIGHT_QUEEN_COLUMN; firstLayer++) {for (int secondLayer = firstLayer + 1; secondLayer < EIGHT_QUEEN_COLUMN; secondLayer++) {if ( ((firstLayer - secondLayer) == (column[firstLayer] - column[secondLayer])) ||  ((firstLayer - secondLayer) == (column[secondLayer] - column[firstLayer])) ) {return false;}}}return true;}}