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Python每日一练(20230502)

1. 被围绕的区域 🌟🌟

2. 两数之和 II 🌟

3. 二叉树展开为链表 🌟🌟

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1. 被围绕的区域

给你一个 m x n 的矩阵 board ，由若干字符 'X' 和 'O' ，找到所有被 'X' 围绕的区域，并将这些区域里所有的 'O' 用 'X' 填充。

示例 1：

Python每日一练(20230502)

输入：board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]
输出：[["X","X","X","X"],["X","X","X","X"],["X","X","X","X"],["X","O","X","X"]]
解释：被围绕的区间不会存在于边界上，换句话说，任何边界上的 'O' 都不会被填充为 'X'。 任何不在边界上，或不与边界上的 'O' 相连的 'O' 最终都会被填充为 'X'。如果两个元素在水平或垂直方向相邻，则称它们是“相连”的。

示例 2：

输入：board = [["X"]]
输出：[["X"]]

提示：

m == board.length
n == board[i].length
1 <= m, n <= 200
board[i][j] 为 'X' 或 'O'

出处：

https://edu.csdn.net/practice/26945724

代码：

from typing import List
class Solution:
    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        if not board or len(board) == 0:
            return
        m = len(board)
        n = len(board[0])
        from collections import deque
        queue = deque()
        for i in range(m):
            if board[i][0] == "O":
                queue.append((i, 0))
            if board[i][n - 1] == "O":
                queue.append((i, n - 1))
        for j in range(n):
            if board[0][j] == "O":
                queue.append((0, j))
            if board[m - 1][j] == "O":
                queue.append((m - 1, j))
        while queue:
            x, y = queue.popleft()
            board[x][y] = "M"
            for nx, ny in [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)]:
                if 0 <= nx < m and 0 <= ny < n and board[nx][ny] == "O":
                    queue.append((nx, ny))
        for i in range(m):
            for j in range(n):
                if board[i][j] == "O":
                    board[i][j] = "X"
                if board[i][j] == "M":
                    board[i][j] = "O"
#%%
s = Solution()
board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]
s.solve(board)
print(board)

输出：

[['X', 'X', 'X', 'X'], ['X', 'X', 'X', 'X'], ['X', 'X', 'X', 'X'], ['X', 'O', 'X', 'X']]

2. 两数之和 II

给定一个已按照 非递减顺序排列 的整数数组 numbers ，请你从数组中找出两个数满足相加之和等于目标数 target 。

函数应该以长度为 2 的整数数组的形式返回这两个数的下标值。numbers 的下标 从 1 开始计数 ，所以答案数组应当满足 1 <= answer[0] < answer[1] <= numbers.length 。

你可以假设每个输入 只对应唯一的答案 ，而且你 不可以 重复使用相同的元素。

示例 1：

输入：numbers = [2,7,11,15], target = 9
输出：[1,2]
解释：2 与 7 之和等于目标数 9 。因此 index1 = 1, index2 = 2 。

示例 2：

输入：numbers = [2,3,4], target = 6
输出：[1,3]

示例 3：

输入：numbers = [-1,0], target = -1
输出：[1,2]

提示：

2 <= numbers.length <= 3 * 10^4
-1000 <= numbers[i] <= 1000
numbers 按 非递减顺序 排列
-1000 <= target <= 1000
仅存在一个有效答案

出处：

https://edu.csdn.net/practice/26945725

代码：

class Solution(object):
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        d = {}
        size = 0
        while size < len(numbers):
            if not numbers[size] in d:
                d[numbers[size]] = size + 1
            if target - numbers[size] in d:
                if d[target - numbers[size]] < size + 1:
                    answer = [d[target - numbers[size]], size + 1]
                    return answer
            size = size + 1
#%%
s = Solution()
print(s.twoSum(numbers = [2,7,11,15], target = 9))
print(s.twoSum(numbers = [2,3,4], target = 6))
print(s.twoSum(numbers = [-1,0], target = -1))

输出：

[1, 2]
[1, 3]
[1, 2]

3. 二叉树展开为链表

给你二叉树的根结点 root ，请你将它展开为一个单链表：

展开后的单链表应该同样使用 TreeNode ，其中 right 子指针指向链表中下一个结点，而左子指针始终为 null 。
展开后的单链表应该与二叉树 先序遍历 顺序相同。

示例 1：

Python每日一练(20230502)

输入：root = [1,2,5,3,4,null,6]
输出：[1,null,2,null,3,null,4,null,5,null,6]

示例 2：

输入：root = []
输出：[]

示例 3：

输入：root = [0]
输出：[0]

提示：

树中结点数在范围 [0, 2000] 内
-100 <= Node.val <= 100

进阶：你可以使用原地算法（O(1) 额外空间）展开这棵树吗？

出处：

https://edu.csdn.net/practice/26945726

代码：

class TreeNode(object):
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

class Solution:
    def flatten(self, root: TreeNode) -> None:
        """
        Do not return anything, modify root in-place instead.
        """
        while root != None:
            if root.left == None:
                root = root.right
            else:
                pre = root.left
                while pre.right != None:
                    pre = pre.right
                pre.right = root.right
                root.right = root.left
                root.left = None
                root = root.right

def listToTree(lst):
    if not lst:
        return None
    root = TreeNode(lst[0])
    queue = [root]
    i = 1
    while i < len(lst):
        node = queue.pop(0)
        if i<len(lst) and lst[i] is not None:
            node.left = TreeNode(lst[i])
            queue.append(node.left)
        i += 1
        if i<len(lst) and lst[i] is not None:
            node.right = TreeNode(lst[i])
            queue.append(node.right)
        i += 1
    return root

def preorderTraversal(root: TreeNode):
    res = []
    if not root:
        return res
    res.append(root.val)
    res.extend(preorderTraversal(root.left))
    res.extend(preorderTraversal(root.right))
    return res

s = Solution()
null = None
nums = [1,2,5,3,4,null,6]
root = listToTree(nums)
s.flatten(root)
print(preorderTraversal(root))

输出：

[1, 2, 3, 4, 5, 6]