feat(0344-reverse-string): add py3 solution

0344_reverse-string/README.md

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+Write a function that reverses a string. The input string is given as an array of characters `s`.
+
+You must do this by modifying the input array [in-place](https://en.wikipedia.org/wiki/In-place_algorithm) with `O(1)` extra memory.
+
+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:
+
+* `1 <= s.length <= 105`
+* `s[i]` is a [printable ascii character](https://en.wikipedia.org/wiki/ASCII#Printable_characters).

0344_reverse-string/python3/solution.py

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