動機

就reverse

Problem

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

 

Example 1:

Input: s = [h,e,l,l,o]Output: [o,l,l,e,h]

Example 2:

Input: s = [H,a,n,n,a,h]Output: [h,a,n,n,a,H]

 

Constraints:

 

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

Sol

class Solution:
    def reverseString(self, s: List[str]) -> None:
        i,j = 0, len(s)-1
        while i < j:
            s[i],s[j] = s[j],s[i]
            i,j = i+1,j-1