# Sudoku Solver – LeetCode Solution Java , Python 3, Python 2 , C , C++, Best and Optimal Solutions , All you need.

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 digits
`1-9`

must occur exactly once in each of the 9`3x3`

sub-boxes of the grid.

The `'.'`

character indicates empty cells.

**Example 1:**

Input:board = [["5","3",".",".","7",".",".",".","."],["6",".",".","1","9","5",".",".","."],[".","9","8",".",".",".",".","6","."],["8",".",".",".","6",".",".",".","3"],["4",".",".","8",".","3",".",".","1"],["7",".",".",".","2",".",".",".","6"],[".","6",".",".",".",".","2","8","."],[".",".",".","4","1","9",".",".","5"],[".",".",".",".","8",".",".","7","9"]]Output:[["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],["4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9","6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4","5","2","8","6","1","7","9"]]Explanation:The input board is shown above and the only valid solution is shown below:

**Constraints:**

`board.length == 9`

`board[i].length == 9`

`board[i][j]`

is a digit or`'.'`

.- It is
**guaranteed**that the input board has only one solution.

# C++ Sudoku Solver LeetCode Solution

```
``````
bool check(vector<vector<char>> &board, int i, int j, char val)
{
int row = i - i%3, column = j - j%3;
for(int x=0; x<9; x++) if(board[x][j] == val) return false;
for(int y=0; y<9; y++) if(board[i][y] == val) return false;
for(int x=0; x<3; x++)
for(int y=0; y<3; y++)
if(board[row+x][column+y] == val) return false;
return true;
}
bool solveSudoku(vector<vector<char>> &board, int i, int j)
{
if(i==9) return true;
if(j==9) return solveSudoku(board, i+1, 0);
if(board[i][j] != '.') return solveSudoku(board, i, j+1);
for(char c='1'; c<='9'; c++)
{
if(check(board, i, j, c))
{
board[i][j] = c;
if(solveSudoku(board, i, j+1)) return true;
board[i][j] = '.';
}
}
return false;
}
```

public:

void solveSudoku(vector<vector>& board) {

solveSudoku(board, 0, 0);

}

# Java Sudoku Solver LeetCode Solution

```
``````
public class Solution {
public void solveSudoku(char[][] board) {
if(board == null || board.length == 0)
return;
solve(board);
}
public boolean solve(char[][] board){
for(int i = 0; i < board.length; i++){
for(int j = 0; j < board[0].length; j++){
if(board[i][j] == '.'){
for(char c = '1'; c <= '9'; c++){//trial. Try 1 through 9
if(isValid(board, i, j, c)){
board[i][j] = c; //Put c for this cell
if(solve(board))
return true; //If it's the solution return true
else
board[i][j] = '.'; //Otherwise go back
}
}
return false;
}
}
}
return true;
}
private boolean isValid(char[][] board, int row, int col, char c){
for(int i = 0; i < 9; i++) {
if(board[i][col] != '.' && board[i][col] == c) return false; //check row
if(board[row][i] != '.' && board[row][i] == c) return false; //check column
if(board[3 * (row / 3) + i / 3][ 3 * (col / 3) + i % 3] != '.' &&
board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) return false; //check 3*3 block
}
return true;
}
}
```

# Python 3 Sudoku Solver LeetCode Solution

```
``````
class Solution:
# @param board, a 9x9 2D array
# Solve the Sudoku by modifying the input board in-place.
# Do not return any value.
def solveSudoku(self, board):
self.board = board
self.solve()
def findUnassigned(self):
for row in range(9):
for col in range(9):
if self.board[row][col] == ".":
return row, col
return -1, -1
def solve(self):
row, col = self.findUnassigned()
#no unassigned position is found, puzzle solved
if row == -1 and col == -1:
return True
for num in ["1","2","3","4","5","6","7","8","9"]:
if self.isSafe(row, col, num):
self.board[row][col] = num
if self.solve():
return True
self.board[row][col] = "."
return False
def isSafe(self, row, col, ch):
boxrow = row - row%3
boxcol = col - col%3
if self.checkrow(row,ch) and self.checkcol(col,ch) and self.checksquare(boxrow, boxcol, ch):
return True
return False
def checkrow(self, row, ch):
for col in range(9):
if self.board[row][col] == ch:
return False
return True
def checkcol(self, col, ch):
for row in range(9):
if self.board[row][col] == ch:
return False
return True
def checksquare(self, row, col, ch):
for r in range(row, row+3):
for c in range(col, col+3):
if self.board[r][c] == ch:
return False
return True
```

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