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Hello Programmers/Coders, Today we are going to share solutions to the Programming problems of LeetCode Solutions in C++, Java, & Python. At Each Problem with Successful submission with all Test Cases Passed, you will get a score or marks and LeetCode Coins. And after solving maximum problems, you will be getting stars. This will highlight your profile to the recruiters.

In this post, you will find the solution for the Sudoku Solver in C++, Java & Python-LeetCode problem. We are providing the correct and tested solutions to coding problems present on LeetCode. If you are not able to solve any problem, then you can take help from our Blog/website.

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About LeetCode

LeetCode is one of the most well-known online judge platforms to help you enhance your skills, expand your knowledge and prepare for technical interviews. 

LeetCode is for software engineers who are looking to practice technical questions and advance their skills. Mastering the questions in each level on LeetCode is a good way to prepare for technical interviews and keep your skills sharp. They also have a repository of solutions with the reasoning behind each step.

LeetCode has over 1,900 questions for you to practice, covering many different programming concepts. Every coding problem has a classification of either EasyMedium, or Hard.

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  • Database
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  • Recursion, etc.

Leetcode has a huge number of test cases and questions from interviews too like Google, Amazon, Microsoft, Facebook, Adobe, Oracle, Linkedin, Goldman Sachs, etc. LeetCode helps you in getting a job in Top MNCs. To crack FAANG Companies, LeetCode problems can help you in building your logic.

Link for the ProblemSudoku Solver– LeetCode Problem

Sudoku Solver– LeetCode Problem

Problem:

Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy all of the following rules:

  1. Each of the digits 1-9 must occur exactly once in each row.
  2. Each of the digits 1-9 must occur exactly once in each column.
  3. 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:

250px Sudoku by L2G 20050714.svg
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:

250px Sudoku by L2G 20050714 solution.svg

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.
Sudoku Solver– LeetCode Solutions
class Solution {
 public:
  void solveSudoku(vector>& board) {
    solve(board, 0);
  }

 private:
  bool solve(vector>& board, int s) {
    if (s == 81)
      return true;

    const int i = s / 9;
    const int j = s % 9;

    if (board[i][j] != '.')
      return solve(board, s + 1);

    for (char c = '1'; c <= '9'; ++c)
      if (isValid(board, i, j, c)) {
        board[i][j] = c;
        if (solve(board, s + 1))
          return true;
        board[i][j] = '.';
      }

    return false;
  }

  bool isValid(vector>& board, int row, int col, char c) {
    for (int i = 0; i < 9; ++i)
      if (board[i][col] == c || board[row][i] == c ||
          board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c)
        return false;
    return true;
  }
};
class Solution {
  public void solveSudoku(char[][] board) {
    dfs(board, 0);
  }

  private boolean dfs(char[][] board, int s) {
    if (s == 81)
      return true;

    final int i = s / 9;
    final int j = s % 9;

    if (board[i][j] != '.')
      return dfs(board, s + 1);

    for (char c = '1'; c <= '9'; ++c)
      if (isValid(board, i, j, c)) {
        board[i][j] = c;
        if (dfs(board, s + 1))
          return true;
        board[i][j] = '.';
      }

    return false;
  }

  private boolean isValid(char[][] board, int row, int col, char c) {
    for (int i = 0; i < 9; ++i)
      if (board[i][col] == c || board[row][i] == c ||
          board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c)
        return false;
    return true;
  }
}
class Solution:
  def solveSudoku(self, board: List[List[str]]) -> None:
    def isValid(row: int, col: int, c: chr) -> bool:
      for i in range(9):
        if board[i][col] == c or 
           board[row][i] == c or 
           board[3 * (row // 3) + i // 3][3 * (col // 3) + i % 3] == c:
          return False
      return True

    def solve(s: int) -> bool:
      if s == 81:
        return True

      i = s // 9
      j = s % 9

      if board[i][j] != '.':
        return solve(s + 1)

      for c in string.digits[1:]:
        if isValid(i, j, c):
          board[i][j] = c
          if solve(s + 1):
            return True
          board[i][j] = '.'

      return False

    solve(0)

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