solution(java): 37. Sudoku Solver

37. Sudoku Solver
- Java

Hard/37.Sudoku Solver/README.md

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+# LeetCode 37.Sudoku Solver
+
+## Problem Description
+
+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:**
+
+![Screenshot 2023-10-31 004422](https://github.com/Bharathlax-2005/LeetCode-3/assets/116173614/b6c6ff39-513d-4295-9b52-90c1a1f5c2c4)
+
+
+**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:
+
+
+![Screenshot 2023-10-31 004607](https://github.com/Bharathlax-2005/LeetCode-3/assets/116173614/ab9cd35f-eed8-45ca-b511-0a88fb7bfd25)
+
+
+**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.
+- 
+### Link
+
+https://leetcode.com/problems/sudoku-solver/

Hard/37.Sudoku Solver/Sol3.java

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+class Solution {
+    public void solveSudoku(char[][] board) {
+        solve(board);
+    }
+
+    private boolean solve(char[][] board) {
+        for (int row = 0; row < 9; row++) {
+            for (int col = 0; col < 9; col++) {
+                if (board[row][col] == '.') {
+                    for (char c = '1'; c <= '9'; c++) {
+                        if (isValid(board, row, col, c)) {
+                            board[row][col] = c;
+                            if (solve(board)) {
+                                return true;
+                            }
+                            board[row][col] = '.'; // Backtrack
+                        }
+                    }
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private boolean isValid(char[][] board, int row, int col, char c) {
+        for (int i = 0; i < 9; i++) {
+            if (board[row][i] == c || board[i][col] == c || board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+