Valid Sudoku Leetcode Solution

In this post, we are going to solve the Valid Sudoku Leetcode Solution problem of Leetcode. This Leetcode problem is done in many programming languages like C++, Java, and Python.

Problem

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the nine 3 x 3 sub–boxes of the grid must contain the digits 1-9 without repetition.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

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: true

Example 2:

Input: board = 
[["8","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: false
Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

Now, let’s see the leetcode solution of Valid Sudoku Leetcode Solution.

Valid Sudoku Leetcode Solution in Python

class Solution:
  def isValidSudoku(self, board: List[List[str]]) -> bool:
    seen = set()

    for i in range(9):
      for j in range(9):
        c = board[i][j]
        if c == '.':
          continue
        if c + '@row ' + str(i) in seen or \
           c + '@col ' + str(j) in seen or \
           c + '@box ' + str(i // 3) + str(j // 3) in seen:
          return False
        seen.add(c + '@row ' + str(i))
        seen.add(c + '@col ' + str(j))
        seen.add(c + '@box ' + str(i // 3) + str(j // 3))

    return True

Valid Sudoku Leetcode Solution in CPP

class Solution {
 public:
  bool isValidSudoku(vector<vector<char>>& board) {
    unordered_set<string> seen;

    for (int i = 0; i < 9; ++i)
      for (int j = 0; j < 9; ++j) {
        if (board[i][j] == '.')
          continue;
        const string c(1, board[i][j]);
        if (!seen.insert(c + "@row" + to_string(i)).second ||
            !seen.insert(c + "@col" + to_string(j)).second ||
            !seen.insert(c + "@box" + to_string(i / 3) + to_string(j / 3))
                 .second)
          return false;
      }

    return true;
  }
};

Valid Sudoku Leetcode Solution in Java

class Solution {
  public boolean isValidSudoku(char[][] board) {
    Set<String> seen = new HashSet<>();

    for (int i = 0; i < 9; ++i)
      for (int j = 0; j < 9; ++j) {
        if (board[i][j] == '.')
          continue;
        final char c = board[i][j];
        if (!seen.add(c + "@row" + i) ||
            !seen.add(c + "@col" + j) ||
            !seen.add(c + "@box" + i / 3 + j / 3))
          return false;
      }

    return true;
  }
}

Note: This problem Valid Sudoku is generated by Leetcode but the solution is provided by Chase2learn This tutorial is only for Educational and Learning purposes.

NEXT: Sudoku Solver Leetcode Solution