Valid Sudoku

01 · Question

Given a 9x9 grid, board, representing a Sudoku, return true if the board does not have any conflicts and false otherwise. The board contains only numbers between 0 and 9 in each cell, with 0's denoting empty cells.

A conflict is a duplicate number (other than 0) along a row, a column, or a 3x3 subgrid.

Example 1:

Input: A valid Sudoku board.
Output: true

Example 2:

Input: A board with duplicates in the first row.
Output: false

02 · Solution

Reference solution

1def isValidSudoku(board: List[List[str]]) -> bool:
2    rows = [set() for _ in range(9)]
3    cols = [set() for _ in range(9)]
4    boxes = [set() for _ in range(9)]
5    
6    for r in range(9):
7        for c in range(9):
8            val = board[r][c]
9            if val == ".":
10                continue
11                
12            # Check row
13            if val in rows[r]: return False
14            rows[r].add(val)
15            
16            # Check col
17            if val in cols[c]: return False
18            cols[c].add(val)
19            
20            # Check box
21            idx = (r // 3) * 3 + (c // 3)
22            if val in boxes[idx]: return False
23            boxes[idx].add(val)
24            
25    return True

Spiral Matrix II

Subgrid Maximums