algorithms/118-pascals-triangle.ipynb

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    "### [杨辉三角](https://leetcode-cn.com/problems/pascals-triangle/)\n",
    "\n",
    "给定一个非负整数`numRows`，生成杨辉三角的前`numRows`行。\n",
    "\n",
    "在杨辉三角中，每个数是它左上方和右上方的数的和。\n",
    "\n",
    "#### 示例:\n",
    "```\n",
    "输入: 5\n",
    "输出:\n",
    "[\n",
    "     [1],\n",
    "    [1,1],\n",
    "   [1,2,1],\n",
    "  [1,3,3,1],\n",
    " [1,4,6,4,1]\n",
    "]\n",
    "```"
   ]
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  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "israeli-fairy",
   "metadata": {},
   "outputs": [],
   "source": [
    "from typing import List\n",
    "\n",
    "def generate(numRows: int) -> List[List[int]]:\n",
    "    if numRows <= 0:\n",
    "        return []\n",
    "    \n",
    "    answers = []\n",
    "    for i in range(numRows):\n",
    "        ans = [1 for _ in range(i + 1)]\n",
    "        for j in range(1, i):\n",
    "            ans[j] = answers[i - 1][j - 1] + answers[i - 1][j]\n",
    "        answers.append(ans)\n",
    "    return answers"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "respiratory-sierra",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]]"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "generate(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "id": "lesser-conducting",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[[1],\n",
       " [1, 1],\n",
       " [1, 2, 1],\n",
       " [1, 3, 3, 1],\n",
       " [1, 4, 6, 4, 1],\n",
       " [1, 5, 10, 10, 5, 1],\n",
       " [1, 6, 15, 20, 15, 6, 1],\n",
       " [1, 7, 21, 35, 35, 21, 7, 1],\n",
       " [1, 8, 28, 56, 70, 56, 28, 8, 1],\n",
       " [1, 9, 36, 84, 126, 126, 84, 36, 9, 1],\n",
       " [1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1]]"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "generate(11)"
   ]
  }
 ],
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