Sudoku Solver

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.

A sudoku puzzle...

 

...and its solution numbers marked in red.

 

public class Solution {
    public void solveSudoku(char[][] board) {
        ArrayList<Integer> array=getArrayList(board);
        DFS(board,array,0);
    }
    
    // store in the '.' location in the array
    public ArrayList<Integer> getArrayList(char [][]board){
        ArrayList<Integer> array=new ArrayList<Integer>();
        for(int i=0;i<9;i++){
            for(int j=0;j<9;j++){
                if(board[i][j]=='.'){
                    array.add(i*9+j);
                }
            }
        }
        return array;
    }
    
    public boolean DFS(char[][]board, ArrayList<Integer> array,int index){
        int len=array.size();
        // 当添的数目等于 '.' 的数目时候 depth到底
        if(index == len)
            return true;
        int data=array.get(index);
        int row=data/9;
        int column=data%9;
        // 将该格填入 1-9
        for(int i=1;i<=9;i++){
            if(isValid(board, row, column, i)){
                board[row][column]=(char) (i+'0');
                if(DFS(board, array, index+1))
                    return true;
                // 如果添入的数不valid，把该格填'.'
                board[row][column]='.';
            }
        }
        return false;
    }
    
    public boolean isValid(char[][]board,int row,int column,int data){
        for(int i=0;i<9;i++){
            if(board[row][i]-'0'==data)
                return false;
            if(board[i][column]-'0'==data)
                return false;
            int row_s=3*(row/3) + i/3; 
            int column_s=3*(column/3) + i%3;
            if(board[row_s][column_s]-'0'==data)
            return false;
        }
        return true;
    }
}