[leetcode] Sudoku Solver

from : https://leetcode.com/problems/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) {        internalSolveSudoku(board);    }        private boolean internalSolveSudoku(char[][] board) {        for (int row = 0; row < 9; ++row) {            for (int col = 0; col < 9; ++col) {                if ('.' == board[row][col]) {                    for (int i = 1; i <= 9; ++i) {                                            board[row][col] = (char) ('0' + i);                                                if (isValidSudoku(board, row, col)) {                            if (internalSolveSudoku(board)) {                                return true;                            }                        }                                                board[row][col] = '.';                    }                                        return false;                }            }        }                return true;    }    private boolean isValidSudoku(char[][] board, int x, int y) {        int row, col;        int v = board[x][y];                // Same value in the same column?        for (row = 0; row < 9; ++row) {            if ((x != row) && (board[row][y] == v)) {                return false;            }        }                // Same value in the same row?        for (col = 0; col < 9; ++col) {            if ((y != col) && (board[x][col] == v)) {                return false;            }        }                // Same value in the 3 * 3 block it belong to?        for (row = (x / 3) * 3; row < (x / 3 + 1) * 3; ++row) {            for (col = (y / 3) * 3; col < (y / 3 + 1) * 3; ++col) {                if ((x != row || y != col) && (board[row][col] == v)) {                    return false;                }            }        }                return true;    }}

public class Solution {    public void solveSudoku(char[][] board) {        fillSudoku(board);    }        private boolean fillSudoku(char[][] bd) {        for(int i=0; i<9; ++i) {            for(int j=0; j<9; ++j) {                if(bd[i][j] == '.') {                    for(int k=1; k<10; ++k) {                        bd[i][j] = (char)('0'+k);                        if(validSudoku(bd, i, j, bd[i][j])) {                            if(fillSudoku(bd)) {                                return true;                            }                        }                        bd[i][j] = '.';                    }                    return false;                }            }        }        return true;    }        private boolean validSudoku(char[][] bd, int x, int y, char k) {        for(int i=0; i<9; ++i) {            if(i != x && k == bd[i][y] || i != y && k == bd[x][i]) {                return false;            }        }        for(int i=x/3*3, li = i+3; i<li; ++i) {            for(int j=y/3*3, lj = j+3; j<lj; ++j) {                if((i != x || j != y) && k == bd[i][j]) {                    return false;                }            }        }        return true;    }    }