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"]

解法：
這題可以很簡單的使用 reverse! 解決， 但是這邊挑戰不使用 reverse 該如何解

第一種方法，建立額外空間紀錄

缺點是會佔用到比較多額外空間

def reverse_string(s)
  len = s.length 
  arr = []
  while len > 0
    arr << s.pop
    len -= 1
  end
  arr
end

第二種方法 直接交換左右兩邊的值

若是陣列長度為奇數，兩邊陣列位置相等表示已交換完成，若陣列長度是偶數，左右數值不會相遇在同一位址，因此當左邊陣列位址將大於右邊陣列位址表示交換完畢。

def reverse_string(s)
    left = 0
    right = s.length - 1
    while left < right
        t = s[left]
        s[left] = s[right]
        s[right] = t
        left += 1
        right -= 1
    end
    s
end