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.
思路1：使用暴力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);
}
}思路2：使用Dancing Links，代码后补。
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