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sudoku_solver.py
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sudoku_solver.py
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def sudoku_solve(board):
row = [set() for _ in range(9)]
col = [set() for _ in range(9)]
box = [set() for _ in range(9)]
remaining = []
for r in range(9):
for c in range(9):
if board[r][c] == '.':
remaining.append((r, c))
else:
n = board[r][c]
b = r // 3 * 3 + c // 3
if (
n in row[r] or
n in col[c] or
n in box[b]
):
return False
row[r].add(n)
col[c].add(n)
box[b].add(n)
def helper():
if not remaining:
return True
r, c = remaining.pop()
b = r // 3 * 3 + c // 3
s = {str(n) for n in range(1, 10)}
s -= row[r]
s -= col[c]
s -= box[b]
if not s:
remaining.append((r, c))
return False
for guess in s:
row[r].add(guess)
col[c].add(guess)
box[b].add(guess)
if helper():
return True
row[r].remove(guess)
col[c].remove(guess)
box[b].remove(guess)
return False
return helper()