【LeetCode 0051】【剪枝】N皇后

51. N-Queens

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle. You may return the answer in any order.

Each solution contains a distinct board configuration of the n-queens’ placement, where 'Q' and '.' both indicate a queen and an empty space, respectively.

Example 1:

**Input:** n = 4
**Output:** [[".Q..","...Q","Q...","..Q."],["..Q.","Q...","...Q",".Q.."]]
**Explanation:** There exist two distinct solutions to the 4-queens puzzle as shown above

Example 2:

**Input:** n = 1
**Output:** [["Q"]]

Constraints:

• 1 <= n <= 9

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