回溯算法之八皇后

public class EightQueens {



/**
* @param args
*/
public static void main(String[] args) {
QueueTrack queueTrack = new QueueTrack(8);
queueTrack.backTrace(1);
System.out.println("可行方案数：" + queueTrack.getSum());
}

}

class QueueTrack {

private int[] lines;
private int lineNum;
private int sum;

public QueueTrack(int lineNum) {
this.lineNum = lineNum;
lines = new int[this.lineNum + 1];
}

public  void backTrace(int lineIndex) {

if (lineIndex > lineNum) {
sum++;
print();
} else {
/*
* 遍历lineIndex行的4列，判断是否满足8皇后存放要求
*/
for (int i = 1; i <= lineNum; i++) {
lines[lineIndex] = i; //假设放到lineIndex行的i列上

if(!judgePlace(lineIndex)) { //判断是否与已存放的皇后存在规则的冲突
backTrace(lineIndex + 1);
}
}
}
}

private  boolean judgePlace(int lineIndex) {

boolean notPlace = false;
for (int i = 1; i < lineIndex; i++ ) {
if (Math.abs(lineIndex - i) == Math.abs(lines[lineIndex] - lines[i])
|| lines[i] == lines[lineIndex]) {
notPlace = true;
break;
}
}
return notPlace;
}

private  void print() {
for (int i = 1; i < 5; i++) {
System.out.println("line is " + i + " column is " + lines[i]);
}

System.out.println("==============================================");
}

public int getSum() {
return this.sum;
}

}