leetcode51. 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.."] ]
class Solution { public: vector<vector<string>> solveNQueens(int n) { vector<vector<string>> res; vector<string> nQueens(n, string(n, '.')); solveNQueens(res, nQueens, 0, n); return res; } private: void solveNQueens(vector<vector<string>>& res, vector<string>& nQueens, int row, int n) { if (row == n) { res.push_back(nQueens); return; } for (int col = 0; col < n; col++) { if (isValid(nQueens, row, col, n)) { nQueens[row][col] = 'Q'; solveNQueens(res,nQueens,row+1,n); nQueens[row][col] = '.'; } } } bool isValid(vector<string>& nQueens, int row, int col, int n) { for (int i = 0; i < row; i++) { if (nQueens[i][col] == 'Q') return false; } for(int i=row-1,j=col-1;i>=0 && j>=0;--i,--j){ if(nQueens[i][j] == 'Q') return false; } for(int i= row-1,j=col+1;i>=0 && j<n;--i,++j){ if(nQueens[i][j] == 'Q') return false; } return true; } };