Python实现的LeetCode数独求解器仅输出部分解，原因是什么？

你的代码仅返回部分解的核心原因是回溯回退步骤存在语法错误，逻辑完全失效：

• 你在递归返回false（当前路径走不通）时的回退代码写的是board[i][j]=="."，这是比较判断语句，不会修改棋盘的值，正确写法应该是赋值语句board[i][j] = "."

因为没有正确回退错误填入的数字，后续的合法性校验会把这些错误值当成已存在的合法值，导致递归提前终止，只能得到部分填充的棋盘。

修复后完整代码 #

class Solution(object):
    def solveSudoku(self, board):
        """
        :type board: List[List[str]]
        :rtype: None Do not return anything, modify board in-place instead.
        """
        def isValid(board, row, col, c):
          nRow = 3*(row//3)
          nCol = 3*(col//3)

          for i in range(9):
            # 检查行
            if board[row][i]==c:
              return False
            # 检查列
            if board[i][col]==c:
              return False
            # 检查3*3宫格
            if board[nRow+(i//3)][nCol+(i%3)]==c:
              return False
          return True


        def solve(board):
          for i in range(len(board)):
            for j in range(len(board)):
              if board[i][j]==".":
                for c in ["1","2","3","4","5","6","7","8","9"]:
                  if isValid(board, i, j, c): 
                    board[i][j]=c
                    if solve(board):
                        return True
                    # 修复回退逻辑，改为赋值操作
                    board[i][j] = "."
                return False
          return True
        solve(board)
        
        
if __name__=='__main__':
  board1 = [["5","3",".",".","7",".",".",".","."],
            ["6",".",".","1","9","5",".",".","."],
            [".","9","8",".",".",".",".","6","."],
            ["8",".",".",".","6",".",".",".","3"],
            ["4",".",".","8",".","3",".",".","1"],
            ["7",".",".",".","2",".",".",".","6"],
            [".","6",".",".",".",".","2","8","."],
            [".",".",".","4","1","9",".",".","5"],
            [".",".",".",".","8",".",".","7","9"]]

  Solution().solveSudoku(board1)
  print(board1)

内容的提问来源于stack exchange，提问作者Mousumi