数独检查条件无法正确评估

Question

我正在尝试为数独检查程序编写代码，但它似乎没有评估条件，并且每次运行它都会返回true。我似乎无法弄清楚我哪里出错。我已经发布了如何检查行，列和网格的代码。请让我知道我哪里出错了，以及我能做些什么来纠正它。

def check_sudoku(grid,counter):
 # check for duplicates in row:   
    for j in range (len(grid)):

        for i in range(len(grid)):
            if grid[j][i] in counter:
                return True
            else:
                counter.append(grid[i][j])


# check for duplicates in columns:
    for i in range(len(grid)):

        for j in range(len(grid)):
            if grid[i][j] in counter:
                return True
            else:
                counter.append(grid[i][j])

    # check for duplicates in every grid:                  
    size = int(math.sqrt(len(grid)))
    for grid_row in range(0,len(grid),size):
        row_rear = grid_row + size
        for grid_col in range(0,len(grid),size):
            col_rear = grid_col + offset


            for i in range(grid_row,row_rear):
                for j in range(grid_col,col_rear):
                    if grid[i][j] in counter:
                        return False
                    else:
                        counter.append(sudoku[i][j])    



def validate(counter,grid):
    if counter != len(grid):
        print('The puzzle is valid!')
    else:
        print('The puzzle is invalid!')