二刷 leetcode（4）

谁践踏了优雅 2022-05-21 12:34 135阅读 0赞

36. 有效的数独

判断一个 9x9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。

1.  数字 `1-9` 在每一行只能出现一次。
2.  数字 `1-9` 在每一列只能出现一次。
3.  数字 `1-9` 在每一个以粗实线分隔的 `3x3` 宫内只能出现一次。

![250px-Sudoku-by-L2G-20050714.svg.png][]

上图是一个部分填充的有效的数独。

数独部分空格内已填入了数字，空白格用 `'.'` 表示。

示例 1:

输入:
    [
      ["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"]
    ]
    输出: true

示例 2:

输入:
    [
      ["8","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"]
    ]
    输出: false
    解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。
         但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。

说明:

*  一个有效的数独（部分已被填充）不一定是可解的。
 *  只需要根据以上规则，验证已经填入的数字是否有效即可。
 *  给定数独序列只包含数字 `1-9` 和字符 `'.'` 。
 *  给定数独永远是 `9x9` 形式的。

代码思路：

先用一个函数判断是不是有效行(列)，同时判断这一行(列)有没有重复的元素。

class Solution:
        def isValidSudoku(self, board):
            """
            :type board: List[List[str]]
            :rtype: bool
            """
            def isValidList(xs):
                xs = list(filter(lambda x: x !="." ,xs))
                return len(set(xs)) == len(xs)
                          
            for i in range(9):
                if not isValidList([board[i][j] for j in range(9)]) or not isValidList([board[j][i] for j in range(9)]):
                    return False
                
            for i in range(3):
                for j in range(3):
                    if not isValidList([board[m][n] for n in range(3 * j, 3 * j + 3) for m in range(3 * i, 3*i+3)]):
                        return False
            return True

367. 有效的完全平方数

给定一个正整数 *num*，编写一个函数，如果 *num* 是一个完全平方数，则返回 True，否则返回 False。

注意：不要使用任何内置的库函数，如 `sqrt`。

示例 1：

输入： 16
    输出： True

示例 2：

输入： 14
    输出： False

代码：前两种方法超时了，第三种方法改进

class Solution:
        def isPerfectSquare(self, num):
            """
            :type num: int
            :rtype: bool
            """
            #### 超出时间限制
    #         if num == 1:
    #             return True
    #         m = num //2
    #         for i in range(m+1):
    #             if i**2 == num:
    #                 return True
    #         return False
    
            #### 通过列举所有的完全平方数，1，4，9，16，25，36，49，64，81，100…等等，
            #### 发现完全平方数的差都为奇数，即1，3，5，7，9，11，13，15…
            #### 等等~所以可以判断完全平方数应该是N个奇数的和。
            #### 超出时间限制
            # if num == 1:
            #     return True
            # for i in range(1, num, 2):
            #     num -= i
            #     if num == 0:
            #         return True
            #     else:
            #         continue
            # return False
            
            left, right = 0, num
            while left < right:
                mid = left + (right - left) // 2
                if mid ** 2 < num:
                    left = mid + 1
                else:
                    right = mid
            if left < 1:
                sqrt_num = left -1
            else:
                sqrt_num = left
            return sqrt_num ** 2 == num

48. 旋转图像

--------------------

给定一个 *n* × *n* 的二维矩阵表示一个图像。

将图像顺时针旋转 90 度。

说明：

你必须在[原地][Link 1]旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要使用另一个矩阵来旋转图像。

示例 1:

给定 matrix = 
    [
      [1,2,3],
      [4,5,6],
      [7,8,9]
    ],
    
    原地旋转输入矩阵，使其变为:
    [
      [7,4,1],
      [8,5,2],
      [9,6,3]
    ]

示例 2:

给定 matrix =
    [
      [ 5, 1, 9,11],
      [ 2, 4, 8,10],
      [13, 3, 6, 7],
      [15,14,12,16]
    ], 
    
    原地旋转输入矩阵，使其变为:
    [
      [15,13, 2, 5],
      [14, 3, 4, 1],
      [12, 6, 8, 9],
      [16, 7,10,11]
    ]

代码：

class Solution:
        def rotate(self, matrix):
            """
            :type matrix: List[List[int]]
            :rtype: void Do not return anything, modify matrix in-place instead.
            """
            ##### the first method
    #         n = len(matrix)
    #         m = n // 2
    #         for i in range(n):
    #             for j in range(n-i-1):
    #                 temp = matrix[i][j]
    #                 matrix[i][j] = matrix[n-j-1][n-i-1]
    #                 matrix[n-j-1][n-i-1] = temp
            
    #         for i in range(m):
    #             for j in range(n):
    #                 temp = matrix[i][j]
    #                 matrix[i][j] = matrix[n-i-1][j]
    #                 matrix[n-i-1][j] = temp
                
            ##### the second method
            n = len(matrix)
            for i in range(n):
                for j in range(i+1, n):
                    matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
            print(matrix)
            for i in range(n):
                matrix[i].reverse()
            print(matrix)

[250px-Sudoku-by-L2G-20050714.svg.png]: https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png
[Link 1]: https://baike.baidu.com/item/%E5%8E%9F%E5%9C%B0%E7%AE%97%E6%B3%95