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math/check_sudoku_board.py

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+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
+
+```
+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.
+
+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
+```
+
+def is_valid_sudoku(board) -> bool:
+        
+  N = 9
+
+  rows = [set() for _ in range(N)]
+  cols = [set() for _ in range(N)]
+  boxes = [set() for _ in range(N)]
+            
+  for r in range(N):
+    for c in range(N):
+      val = board[r][c]
+      if val == '.':
+        continue
+                
+      if val in rows[r]:
+        return False
+      rows[r].add(val)
+
+      if val in cols[c]:
+        return False
+      cols[c].add(val)
+
+      index = (r // 3) * 3 + c // 3
+      if val in boxes[index]:
+        return False
+      boxes[index].add(val)
+        
+  return True