leetcode 51. N-Queens

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

Given an integer n, return all distinct solutions to the n-queens puzzle.

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

For example,
There exist two distinct solutions to the 4-queens puzzle:

[
 [".Q..",  // Solution 1
  "...Q",
  "Q...",
  "..Q."],

 ["..Q.",  // Solution 2
  "Q...",
  "...Q",
  ".Q.."]
]

这个哥以前就解过了，大概一年前吧，偷懒了，直接粘过来了。

typedef unsigned char BYTE;
class Solution {
	int N;
	vector<vector<BYTE>> chess_board;
	deque<deque<BYTE>>record, solution;
	deque<BYTE>cc;
	deque<BYTE>bb;
	bool update(int height)
	{
		cc.clear();
		chess_board[height][bb[height]] = 1;
		for (int i = 0; i < N; i++)
		{
			chess_board[height][i] = 1;
			chess_board[i][bb[height]] = 1;
			if (height - bb[height] + i >= 0 && height - bb[height] + i <= N - 1)
				chess_board[height - bb[height] + i][i] = 1;
			if (height + bb[height] - i >= 0 && height + bb[height] - i <= N - 1)//右上左下  
				chess_board[height + bb[height] - i][i] = 1;
		}
		for (int i = 0; i < N; i++)
			if (chess_board[height + 1][i] == 0)
				cc.push_back(i);
		if (!cc.empty())
			return true;
		return false;
	}

	void eight_queen()
	{
		for (int i = 0; i < N; i++)
			bb.push_back(i);
		record.push_back(bb);
		bb.clear();
		int k = 0;
		while (k < N)
		{
			if (!record.empty())
			{
				if (record[k].empty())
				{
					while (record[k].empty())
					{
						record.pop_back();
						if (record.empty())
							return;
						bb.pop_back();
						k--;
					}
					for (int i = 0; i < N; i++)
						for (int j = 0; j < N; j++)
							chess_board[i][j] = 0;
					for (int i = 0; i < k; i++)
						update(i);
				}
				bb.push_back(record[k][0]);
				record[k].pop_front();
			}
			if (!update(k))
			{
				while (!update(k))
				{
					if (record[k].empty())
					{
						while (record[k].empty())
						{
							record.pop_back();
							if (record.empty())
								return;
							k--;
							for (int i = 0; i < N; i++)
								for (int j = 0; j < N; j++)
									chess_board[i][j] = 0;
							for (int i = 0; i < k; i++)
								update(i);
							bb.pop_back();
						}
						bb.pop_back();
						break;
					}
					else
					{
						bb[k] = record[k][0];
						record[k].pop_front();
						for (int i = 0; i < N; i++)
							for (int j = 0; j < N; j++)
								chess_board[i][j] = 0;
						for (int i = 0; i < k; i++)
							update(i);
						if (update(k))
						{
							if (k == N - 2)
							{
								deque<BYTE> dd;
								dd = bb;
								dd.push_back(0);
								for (int i = 0; i < cc.size(); i++)
								{
									dd[N - 1] = cc[i];
									solution.push_back(dd);
								}
								bb.pop_back();
								for (int i = 0; i < N; i++)
									for (int j = 0; j < N; j++)
										chess_board[i][j] = 0;
								for (int i = 0; i < k; i++)
									update(i);
							}
							else
							{
								record.push_back(cc);
								k++;
							}
							break;
						}
					}

				}
			}
			else
			{
				if (k == N - 2)
				{
					deque<BYTE> dd;
					dd = bb;
					dd.push_back(0);
					for (int i = 0; i < cc.size(); i++)
					{
						dd[N - 1] = cc[i];
						solution.push_back(dd);
					}
					bb.pop_back();
					for (int i = 0; i < N; i++)
						for (int j = 0; j < N; j++)
							chess_board[i][j] = 0;
					for (int i = 0; i < k; i++)
						update(i);
				}
				else
				{
					record.push_back(cc);
					k++;
				}
			}
		}
	}
public:
	vector<vector<string>> solveNQueens(int n) {
		vector<vector<string>>re;
		if (n == 1)
		{
			vector<string>v;
			v.push_back("Q");
			re.push_back(v);
			return re;
		}
		N = n;
		chess_board.resize(N);
		for (int i = 0; i < N; i++)
			chess_board[i].resize(N);
		eight_queen();
		string s = string(N, '.');
		vector<string> ss(N, s);
		for (int i = 0; i < solution.size(); i++)
		{
			vector<string>aa = ss;
			for (int j = 0; j < N; j++)
				aa[j][solution[i][j]] = 'Q';
			re.push_back(aa);
		}
		return re;
	}
};

accept

后面52. N-Queens II返回size大小就行了，一样AC