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package leetcode.digui;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class N051Nqueue {
public static void main(String[] args) {
new N051Nqueue().solveNQueens(4);
}
List<List<String>> res = new ArrayList<>();
public List<List<String>> solveNQueens(int n) {
if(n < 1){
return res;
}
List<Integer> list = new ArrayList<>();
help(0,n,list);
return res;
}
private void help(int row, int n, List<Integer> list){
if(row == n){
List<String> strList = new ArrayList<>();
for(Integer num:list){
char[] t = new char[n];
Arrays.fill(t,'.');
t[num] = 'Q';
strList.add(new String(t));
}
res.add(strList);
return;
}
//每一列都尝试一下
for (int col = 0; col < n; col++) {
//当前列是否合法
if (!list.contains(col)) {
//左斜与右协是否哈法
if(!isDiagonalAttack(list,col)){
list.add(col);
help(row+1,n,list);
//回溯
list.remove(list.size()-1);
}
}
}
}
private boolean isDiagonalAttack(List<Integer> currentQueen, int i) {
int currentRow = currentQueen.size();
int currentCol = i;
//判断每一行的皇后的情况
for (int row = 0; row < currentQueen.size(); row++) {
//左上角的对角线和右上角的对角线，差要么相等，要么互为相反数，直接写成了绝对值
if (Math.abs(currentRow - row) == Math.abs(currentCol - currentQueen.get(row))) {
return true;
}
}
return false;
}
}