python 九宫格

Python九宫格是一个常见的编程练习题，它要求在一个3x3的方格中填入1到9的数字，使得每行、每列和对角线上的数字之和都相等。下面是一个简单的Python代码示例来解决九宫格问题：

def is_valid(grid):
    # 检查每行的和是否相等
    row_sum = sum(grid[0])
    for row in grid:
        if sum(row) != row_sum:
            return False
    
    # 检查每列的和是否相等
    for col in range(3):
        col_sum = sum(grid[row][col] for row in range(3))
        if col_sum != row_sum:
            return False
    
    # 检查对角线的和是否相等
    diagonal_sum1 = grid[0][0] + grid[1][1] + grid[2][2]
    diagonal_sum2 = grid[0][2] + grid[1][1] + grid[2][0]
    if diagonal_sum1 != row_sum or diagonal_sum2 != row_sum:
        return False
    
    return True

def solve_sudoku():
    grid = [[0] * 3 for _ in range(3)]
    numbers = list(range(1, 10))
    
    def backtrack(row, col):
        if row == 3:
            if is_valid(grid):
                return True
            return False
        
        next_row = row + 1 if col == 2 else row
        next_col = (col + 1) % 3
        
        for num in numbers:
            if num not in grid[row] and num not in [grid[i][col] for i in range(row)]:
                grid[row][col] = num
                if backtrack(next_row, next_col):
                    return True
                grid[row][col] = 0
        
        return False
    
    if backtrack(0, 0):
        for row in grid:
            print(row)
    else:
        print("No solution found.")

solve_sudoku()

这段代码使用回溯算法来解决九宫格问题。它首先定义了一个`is_valid`函数来检查当前九宫格是否满足条件，然后定义了一个`backtrack`函数来递归地尝试填入数字。最后，调用`solve_sudoku`函数来解决九宫格问题并打印结果。