1 class Solution { 2 public: 3     void solveSudoku(vector<vector<char> > &board) { 4         dfs(board, 0, 0); 5     } 6     bool dfs(vector<vector<char>> &board,int i,int j) 7     { 8         if (j >= 9) return dfs(board,i+1,0); 9         if (i == 9) return true;10         if (board[i][j] == ‘.‘)11         {12             for (int k = 1; k <= 9; k++)13             {14                 board[i][j] = char(k + ‘0‘);15                 if (isValid(board, i, j))16                 {17                     if (dfs(board, i, j + 1)) return true;18                 }19                 board[i][j] = ‘.‘;20             }21         }22         else return dfs(board,i,j+1);23         return false;24     }25     bool isValid(vector<vector<char>> &board,int i,int j)//在board作为参数时，有&和没&，时间效率差别非常大！！！26     {27         for (int k = 0; k < 9; k++)28         {29             if (k != j&&board[i][j] == board[i][k]) return false;30         }31         for (int k = 0; k < 9; k++)32         {33             if (k != i&&board[i][j] == board[k][j]) return false;34         }35         for (int row = i / 3 * 3; row < i / 3 * 3 + 3; row++)//(i,j)所在的小九宫格36         {37             for (int col = j / 3 * 3; col < j / 3 * 3 + 3; col++)38             {39                 if ((row != i || col != j) && board[i][j] == board[row][col])40                     return false;41             }42         }43         return true;44     }45 };