[chore] update approach, add type checking

strings/reverse_string_words.ipynb

@@ -11,19 +11,30 @@
     "Follow-up: given a mutable string representation, can you perform this operation in-place?"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Approach \n",
+    "\n",
+    "Since strings are immutable, a mutable string can be represented as a list of characters in a buffer e.g  `['h','e','l','l','o',' ','w','o','r','l','d']` == 'hello world'\n",
+    "\n",
+    "First we reverse entire string to get `'dlrow olleh'`, then we reverse each word within the string to obtain original words."
+   ]
+  },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": 36,
    "metadata": {},
    "outputs": [],
    "source": [
-    "def reverse(string_list: str, start: int, end: int) -> str:\n",
+    "def reverse(string_list: list, start: int, end: int) -> str:\n",
     "    while start < end:\n",
     "        string_list[start], string_list[end] = string_list[end], string_list[start]\n",
     "        start += 1\n",
     "        end -= 1\n",
     "\n",
-    "def reverse_words(string_list):\n",
+    "def reverse_words(string_list: list) -> str:\n",
     "    reverse(string_list, 0, len(string_list) - 1)\n",
     "    start = 0\n",
     "    for i in range(len(string_list)):\n",
@@ -37,22 +48,23 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": 38,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "'there hi'"
+       "'there hello well'"
       ]
      },
-     "execution_count": 29,
+     "execution_count": 38,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "reverse_words(list(\"hi there\"))"
+    "string_list = list(\"well hello there\")\n",
+    "reverse_words(string_list)"
    ]
   },
   {