Create Day-20_Valid_Sudoku.py

Author: Ram-95

Leetcode_30day_challenge/August_Challenge_2021/Day-20_Valid_Sudoku.py

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+# My Solution - O(N^2)
+class Solution:
+    def isValidSudoku(self, board: List[List[str]]) -> bool:
+        rows, cols = 9, 9
+        # Check the Rows
+        for i in range(rows):
+            s = set()
+            for j in range(cols):
+                if board[i][j] in s and board[i][j] != '.':
+                    return False
+                s.add(board[i][j])
+        
+        # Check the Cols
+        for i in range(cols):
+            s = set()
+            for j in range(rows):
+                if board[j][i] in s and board[j][i] != '.':
+                    return False
+                s.add(board[j][i])
+        
+        # Check the Submatrices
+        for i in range(0,9,3):
+            for j in range(9):
+                if j%3 == 0:
+                    ss = set()   
+                for el in board[j][i:i+3]:
+                    if el != '.' and el in ss:
+                        return False
+                    else:
+                        ss.add(el)
+        return True
+
+
+# A Better approach
+class Solution:
+    def isValidSudoku(self, board: List[List[str]]) -> bool:
+        seen = {}
+        for row in range(9):
+            for col in range(9):
+                val = board[row][col]
+                if val == '.':
+                    continue
+                if (val,'r',row) in seen:
+                    return False
+                if (val,'c',col) in seen:
+                    return False
+                if (val,row//3,col//3) in seen:
+                    return False
+                seen[(val,'r',row)] =True
+                seen[(val,'c',col)]=True
+                seen[(val,row//3,col//3)]=True
+        return True