Write a program to solve a Sudoku puzzle by filling the empty cells.
A sudoku solution must satisfy all of the following rules:
- Each of the digits 1-9 must occur exactly once in each row.
- Each of the digits 1-9 must occur exactly once in each column.
- Each of the the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.
Empty cells are indicated by the character ‘.’.
A sudoku puzzle…
…and its solution numbers marked in red.
Note
- The given board contain only digits 1-9 and the character ‘.’.
- You may assume that the given Sudoku puzzle will have a single unique solution.
- The given board size is always 9x9.
Code
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private boolean[][] row = new boolean[9][9];
private boolean[][] col = new boolean[9][9];
private boolean[][] cell = new boolean[9][9];
public void (char[][] board) {
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
if (board[i][j] == '.')
continue;
int num = board[i][j] - '1';
row[i][num] = true;
col[j][num] = true;
cell[(i / 3) * 3 + (j / 3)][num] = true;
}
}
helper(board, 0);
}
private boolean helper(char[][] board, int pos) {
if (pos == 81)
return true;
int x = pos / 9;
int y = pos % 9;
if (board[x][y] != '.')
return helper(board, pos + 1);
for (int k = 0; k < 9; k++) {
int p = (x / 3) * 3 + (y / 3);
if (!row[x][k] && !col[y][k] && !cell[p][k]) {
board[x][y] = (char) (k + 1 + '0');
row[x][k] = true;
col[y][k] = true;
cell[p][k] = true;
if (helper(board, pos + 1))
return true;
board[x][y] = '.';
row[x][k] = false;
col[y][k] = false;
cell[p][k] = false;
}
}
return false;
}
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