LeetCode N-Queens

N-Queens

The n-queens puzzle is the problem of placing n queens on ann×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.."]
]

这个自己做的很好!
class Solution {
public:
    vector<vector<string> > solveNQueens(int n) {
		vector<vector<string> > ret;
        vector<int> result(n);
		dfs(ret, result, 0);
		return ret;
    }

	void dfs(vector<vector<string> >&ret, vector<int>& result, int cur)
	{
		if(result.size() == cur)
		{
			ret.push_back(vector<string>());
			for(int i = 0; i < result.size(); ++i)
			{
				stringstream oss;
				for(int idx = 0; idx < result.size(); ++idx)
					oss << (idx == result[i]? 'Q': '.');
				ret.back().push_back(oss.str());
			}
		}
		else
		{
			for(int i = 0; i < result.size(); ++i)
			{
				if(isOK(result, cur, i))
				{
					result[cur] = i;
					dfs(ret, result, cur+1);
				}
			}
		}
	}

	bool isOK(vector<int>& result, int cur, int val)
	{
		for(int i = 0; i < cur; ++i)
		{
			if(val == result[i])
				return false;
			else if(abs(val - result[i]) == abs(i - cur))
				return false;
		}
		return true;
	}
};



你可能感兴趣的:(Integer,Class,each)