leetcode52. N-Queens II
Follow up for N-Queens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.
class Solution { public: int totalNQueens(int n) { int res = 0; vector<string> nQueens(n, string(n, '.')); dfs(res, nQueens, 0, n); return res; } private: void dfs(int& res, vector<string>& nQueens, int row, int n) { if (row == n) { res++; return; } for (int col = 0; col < n; col++) { if(isValid(nQueens,row,col,n)){ nQueens[row][col] = 'Q'; dfs(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; } };