因為這系列做起來很快，所以就索性一次貼在一篇文了！
PART 1－344. Reverse String (Easy)
不需要回傳一個 list，只需更改 s 即可！
同時，題目要求：in-place 的去做 swap
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"]
更偷懶的！直接 call 內建 function！
PART 2 - 541. Reverse String II (Easy)
Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.
If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.
題目看了霧煞煞，直接看範例
Example 1:
Input: s = "abcdefg", k = 2 Output: "bacdfeg"
Example 2:
Input: s = "abcd", k = 2 Output: "bacd"
懂了嗎？就是要每 2k 個字元中，前 k 個字元做 reverse。
另外，也分享一些還不錯的網民做法：（遞迴）
PART 3 - 557. Reverse Words in a String III (Easy)
Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
Example 1:
Input: s = "Let's take LeetCode contest" Output: "s'teL ekat edoCteeL tsetnoc"
Example 2:
Input: s = "God Ding" Output: "doG gniD"
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