Leetcode 36 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.

Idea 1: use violent DFS

public class Solution {private boolean isValidSudoku(char[][] board, int row, int column) {int i, j;int[] valid1 = new int[10];int[] valid2 = new int[10];int[] valid3 = new int[10];for (i = 0; i <9; i++) {if (board[i][column] != '.') {if (valid1[board[i][column] - '0'] > 0)return false;valid1[board[i][column] - '0']++;}if (board[row][i] != '.') {if (valid2[board[row][i] - '0'] > 0)return false;valid2[board[row][i] - '0']++;}}for (i = (row / 3) * 3; i < (row / 3 + 1) * 3; i++) {for (j = (column / 3) * 3; j < (column / 3 + 1) * 3; j++) {if (board[i][j] != '.') {if (valid3[board[i][j] - '0'] > 0)return false;valid3[board[i][j] - '0']++;}}}return true;}private boolean internalSolveSudoku(char[][] board) {for (int i = 0; i < 9; i++) {for (int j = 0; j < 9; j++) {if (board[i][j] == '.') {for (int k = 1; k <= 9; k++) {board[i][j] = (char) ('0' + k);if (isValidSudoku(board, i, j)) {if (internalSolveSudoku(board)) {return true;}}board[i][j] = '.';                        return false;}}}}return true;}public void solveSudoku(char[][] board) {internalSolveSudoku(board);}}

Idea 2: Use dancing links to complete the code.

Leetcode 36 Sudoku Solver