LeetCode 37 Sudoku Solver（求解数独）

package leetcode_50;

/***
*
* @author pengfei_zheng
* 求解数独问题
*/
public class Solution37 {
public static void solveSudoku(char[][] board) {
if(board==null ||board.length ==0)
return;
else
solve(board);
}

private static boolean solve(char[][] board) {
for(int i = 0 ; i < 9;i++){
for(int j = 0 ; j < 9;j++){
if(board[i][j]=='.'){
for(char c = '1'; c<='9';c++){
if(isValid(board,i,j,c)){
board[i][j]=c;
if(solve(board))
return true;
else
board[i][j]='.';
}
}
return false;
}
}
}
return true;
}

private static boolean isValid(char[][] board, int row, int column, char c) {
for(int i = 0 ; i < 9; i ++){
if(board[row][i]==c) return false;
if(board[i][column]==c) return false;
if(board[3 * (row / 3) + i / 3][ 3 * (column / 3) + i % 3] != '.' &&
board[3 * (row / 3) + i / 3][3 * (column / 3) + i % 3] == c) return false; //check 3*3 block
}
return true;
}
public static void main(String[]args){
long start = System.currentTimeMillis();
char[][] board={{'8','.','.','.','.','.','.','.','.'},
{'.','.','3','6','.','.','.','.','.'},
{'.','7','.','.','9','.','2','.','.'},
{'.','5','.','.','.','7','.','.','.'},
{'.','.','.','.','4','.','7','.','.'},
{'.','.','.','1','.','5','.','3','.'},
{'.','.','1','.','.','.','.','6','8'},
{'.','.','8','5','.','.','.','1','.'},
{'.','9','.','.','.','.','4','.','.'}
};
solveSudoku(board);
long end = System.currentTimeMillis();
for(int i = 0 ; i < 9 ; i ++){
for(int j = 0 ; j < 9 ;j ++){
System.out.print(board[i][j]+" ");
}
System.out.println();
}
System.out.println("耗时: "+ (double)(end-start)/1000+" s");
}
}