syphh

def is_valid(grid, r, c, k):
    not_in_row = k not in grid[r]
    not_in_column = k not in [grid[i][c] for i in range(9)]
    not_in_box = k not in [grid[i][j] for i in range(r//3*3, r//3*3+3) for j in range(c//3*3, c//3*3+3)]
    return not_in_row and not_in_column and not_in_box


def solve(grid, r=0, c=0):
    if r == 9:
        return True