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    "<h1>67. Add Binary</h1>\n",
    "<hr>\n",
    "\n",
    "<!--Copy Paste Leetcode statement between-->\n",
    "<p>Given two binary strings <code>a</code> and <code>b</code>, return <em>their sum as a binary string</em>.</p>\n",
    "\n",
    "<p>&nbsp;</p>\n",
    "<p><strong>Example 1:</strong></p>\n",
    "<pre><strong>Input:</strong> a = \"11\", b = \"1\"\n",
    "<strong>Output:</strong> \"100\"\n",
    "</pre><p><strong>Example 2:</strong></p>\n",
    "<pre><strong>Input:</strong> a = \"1010\", b = \"1011\"\n",
    "<strong>Output:</strong> \"10101\"\n",
    "</pre>\n",
    "<p>&nbsp;</p>\n",
    "<p><strong>Constraints:</strong></p>\n",
    "\n",
    "<ul>\n",
    "\t<li><code>1 &lt;= a.length, b.length &lt;= 10<sup>4</sup></code></li>\n",
    "\t<li><code>a</code> and <code>b</code> consist&nbsp;only of <code>'0'</code> or <code>'1'</code> characters.</li>\n",
    "\t<li>Each string does not contain leading zeros except for the zero itself.</li>\n",
    "</ul>\n",
    "<!--Copy Paste Leetcode statement between-->\n",
    "\n",
    "<p>&nbsp;</p>\n",
    "<a href=\"https://leetcode.com/problems/add-binary/\">Source</a> \n",
    "<hr>\n",
    "\n",
    "<h4>Code</h4>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_binary(a, b):\n",
    "    \"\"\"Cheating method.\"\"\"\n",
    "    return bin(int(a, 2) + int(b, 2))[2:]  # int('s', n) --> convert 's' into number base n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add_binary(a, b):\n",
    "    pos1 = len(a)-1\n",
    "    pos2 = len(b)-1\n",
    "    carry = 0\n",
    "    result = \"\"\n",
    "    while carry or pos1 >= 0 or pos2 >= 0:\n",
    "        s1 = 0 if pos1 < 0 else int(a[pos1])\n",
    "        s2 = 0 if pos2 < 0 else int(b[pos2])\n",
    "        result += str((s1 + s2 + carry) % 2)\n",
    "        carry = (s1 + s2 + carry) // 2\n",
    "        pos1 -= 1\n",
    "        pos2 -= 1\n",
    "    return result[::-1]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<h4>Check</h4>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'100'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = \"11\"\n",
    "b = \"1\"\n",
    "add_binary(a, b)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'10101'"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = \"1010\"\n",
    "b = \"1011\"\n",
    "add_binary(a, b)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'1100'"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = \"1\"\n",
    "b = \"1011\"\n",
    "add_binary(a, b)"
   ]
  }
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