day 20

Author: sachuverma

Leetcode Daily Challenge/August-2021/20. Valid Sudoku.cpp

@@ -0,0 +1,97 @@
+/*
+Valid Sudoku
+============
+
+Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
+
+Each row must contain the digits 1-9 without repetition.
+Each column must contain the digits 1-9 without repetition.
+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 or '.'.
+*/
+
+class Solution
+{
+public:
+    bool valid(vector<vector<char>> &board, int r, int c, char val)
+    {
+        for (int i = 0; i < 9; ++i)
+            if (board[i][c] == val || board[r][i] == val)
+            {
+                return false;
+            }
+
+        for (int i = 0; i < 3; ++i)
+        {
+            for (int j = 0; j < 3; ++j)
+            {
+                if (board[(r / 3) * 3 + i][(c / 3) * 3 + j] == val)
+                {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
+    bool isValidSudoku(vector<vector<char>> board)
+    {
+        for (int i = 0; i < board.size(); ++i)
+        {
+            for (int j = 0; j < board[0].size(); ++j)
+            {
+
+                if (board[i][j] != '.')
+                {
+                    char ch = board[i][j];
+                    board[i][j] = '!';
+
+                    if (!valid(board, i, j, ch))
+                    {
+                        return false;
+                    }
+
+                    board[i][j] = ch;
+                }
+            }
+        }
+
+        return true;
+    }
+};

Leetcode Daily Challenge/August-2021/README.md

@@ -21,3 +21,4 @@
 | 17. | [Count Good Nodes in Binary Tree](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/615/week-3-august-15th-august-21st/3899/)         |     [cpp](./17.%20Count%20Good%20Nodes%20in%20Binary%20Tree.cpp)     |
 | 18. | [Decode Ways](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/615/week-3-august-15th-august-21st/3902/)                             |                   [cpp](./18.%20Decode%20Ways.cpp)                   |
 | 19. | [Maximum Product of Splitted Binary Tree](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/615/week-3-august-15th-august-21st/3903/) | [cpp](./19.%20Maximum%20Product%20of%20Splitted%20Binary%20Tree.cpp) |
+| 20. | [Valid Sudoku](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/615/week-3-august-15th-august-21st/3904/)                            |                  [cpp](./20.%20Valid%20Sudoku.cpp)                   |