344. Reverse String

描述

Write a function that reverses a string. The input string is given as an array of characters char[].

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

You may assume all the characters consist of printable ascii characters.

Example 1:

'''text Input: ["h","e","l","l","o"] Output: ["o","l","l","e","h"] '''

Example 2:

'''text Input: ["H","a","n","n","a","h"] Output: ["h","a","n","n","a","H"] '''

解法

只要注意是原地翻转就好了。

内建方法

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        s.reverse()

两根指针

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        l, r = 0, len(s) - 1

        while l < r:
            s[l], s[r] = s[r], s[l]
            l += 1
            r -= 1

pythonic

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        s[:] = s[::-1]

时间复杂度和空间复杂度都是$O(n)$。