LeetCode 52. NQueens II
撰写于 20171107 修改于 20171107 分类 LeetCode
Question
Follow up for NQueens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.
Solution
Same as NQueens problem, it is a classical algorithm problem but it is not easy for newbies. To tackle this problem, we can go row by row, and in each position on each row, we can check if the current position is safe to place. So the rules are
 if there are no Queens in vertical and horizontal direction, it is safe
 if there are no Queens in 45 diagonal direction, it is safe
 if there are no Queens in 135 diagonal direction, it is safe
And if there are no positions safe to place a Queen, return to the previous row and move onward to choose a new position in that row.
And you can watch this videoN Queen Problem Using Backtracking Algorithm on YouTube to know more about NQueen problems.
Accepted Code


Note that in Python, if you want to deep copy a list, try my_list[:]
by slicing it.