[LeetCode Python3] 37. Sudoku Solver

最新推荐文章于 2020-12-05 18:48:47 发布

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本文介绍了一种使用回溯法解决数独问题的Python算法。通过定义一个Solution类，实现getelements方法获取当前格子所在行、列及九宫格内的元素集合，以及trackback方法进行递归求解。该算法在数独盘面中查找空格并尝试填入数字，直至找到解决方案。

Python3 Solution

class Solution:
    def getelements(self, board, i, j):
        res = set()
        for k in range(9):
            res.add(board[k][j])
        for k in range(9):
            res.add(board[i][k])
        indexa = i // 3 * 3
        indexb = j // 3 * 3
        for ii in range(indexa, indexa+3):
            for jj in range(indexb, indexb+3):
                res.add(board[ii][jj])
        return res

    def trackback(self, board, ia, jb):
        if ia == 8 and jb == 8:
            return True
        for i in range(9):
            for j in range(9):
                if board[i][j] != ".":
                    continue
                tmp = self.getelements(board, i, j)
                for k in range(1, 10):
                    if str(k) in tmp:
                        continue
                    else:
                        board[i][j] = str(k)
                        if self.trackback(board, i, j):
                            return True
                        board[i][j] = "."
                return False
        return True

    def solveSudoku(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        self.trackback(board, 0, 0)