NQueuesII
NQueuesII.java 源码
package algorithm.backtracking.leetcode;
import java.util.HashSet;
import java.util.Set;
/**
* N皇后问题II
*/
public class NQueuesII {
private final Set<Integer> shu = new HashSet<>();
private final Set<Integer> pie = new HashSet<>();
private final Set<Integer> na = new HashSet<>();
private int res = 0;
/**
* 原始的解法
*/
public int totalNQueens1(int n) {
helper(n, 0);
return res;
}
private void helper(int n, int row) {
if (row == n) {
res++;
return;
}
for (int col = 0; col < n; col++) {
if (!shu.contains(col) && !pie.contains(row - col) && !na.contains(row + col)) {
shu.add(col);
pie.add(row - col);
na.add(row + col);
helper(n, row + 1);
shu.remove(col);
pie.remove(row - col);
na.remove(row + col);
}
}
}
}
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