# 杨辉三角

<p>给定一个非负整数 <em><code>numRows</code>，</em>生成「杨辉三角」的前 <em><code>numRows</code> </em>行。</p>

<p><small>在「杨辉三角」中，每个数是它左上方和右上方的数的和。</small></p>

<p><img alt="" src="https://img-service.csdnimg.cn/img_convert/53cb4e7f630b8a991ebd02133e79a9c8.gif" /></p>

<p> </p>

<p><strong>示例 1:</strong></p>

<pre>
<strong>输入:</strong> numRows = 5
<strong>输出:</strong> [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
</pre>

<p><strong>示例 2:</strong></p>

<pre>
<strong>输入:</strong> numRows = 1
<strong>输出:</strong> [[1]]
</pre>

<p> </p>

<p><strong>提示:</strong></p>

<ul>
	<li><code>1 <= numRows <= 30</code></li>
</ul>


## template

```cpp
#include <bits/stdc++.h>
using namespace std;

class Solution
{
public:
    vector<vector<int>> generate(int numRows)
    {

        if (numRows <= 0)
        {
            return {};
        }
        if (numRows == 1)
        {
            return {{1}};
        }
        if (numRows == 2)
        {
            return {{1}, {1, 1}};
        }

        vector<vector<int>> res = {{1}, {1, 1}};
        vector<int> arr;
        int row = 1;
        while (row < numRows - 1)
        {
            arr.push_back(1);
            for (int i = 0; i < res[row].size() - 1; i++)
            {
                int temp = 0;
                temp = res[row][i] + res[row][i + 1];
                arr.push_back(temp);
            }
            arr.push_back(1);
            res.push_back(arr);
            arr.clear();
            row++;
        }
        return res;
    }
};
```

## 答案

```cpp

```

## 选项

### A

```cpp

```

### B

```cpp

```

### C

```cpp

```