Sudoku Solver

Sudoku Solver

问题：

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

思路：

　　常见的回溯模板

我的代码：

public class Solution {
    public void solveSudoku(char[][] board) {
        if(board == null || board.length == 0 || board[0].length == 0)  return;
        placeSudoku(board);
    }
    public boolean placeSudoku(char[][] board)
    {
        for(int i = 0; i < 9; i++)
        {
            for(int j = 0; j < 9; j++)
            {
                if(board[i][j] == '.')
                {
                    for(char k = '1'; k <= '9'; k++)
                    {
                        if(canPut(board, i, j, k))
                        {
                            board[i][j] = k;
                            if(placeSudoku(board))
                                return true;
                            board[i][j] = '.';
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
    public boolean canPut(char[][] board, int i, int j, char c) {
        for(int k = 0; k < 9; k++)
        {
            if((board[i][k] == c && k != j) || (board[k][j] == c && k != i))    return false;
        }
        //test box
        int boxRow = i/3;
        int boxCol = j/3;
        for(int m = boxRow * 3; m < boxRow * 3 + 3; m++)
        {
            for(int n = boxCol * 3; n < boxCol * 3 + 3; n++)
            {
                if(board[m][n] == '.' || (m == i && n == j))  continue;
                else
                {
                    if(board[m][n] == c)    return false;
                }
            }
        }
        return true;
    }
}

学习之处：

• 还是使用之前总结的回溯模板，就是return true和return false地方稍微换了一下。
• 第一遍刷Sudoku Solver 四次通过，这次竟然>4次，汗颜。。。越来手速越不给力了，实验室写代码果然不适合集中精力啊。