# [Pascal's Triangle][title]

## Description

Given a non-negative integer *numRows*, generate the first *numRows* of Pascal's triangle.

![img](https://upload.wikimedia.org/wikipedia/commons/0/0d/PascalTriangleAnimated2.gif)
In Pascal's triangle, each number is the sum of the two numbers directly above it.

**Example:**

```
Input: 5
Output:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]
```

**Tags:** Array


## 思路

题意是给出行数，输出帕斯卡尔三角形，很简单的模拟，就不多说了。

```java
class Solution {
    public List<List<Integer>> generate(int numRows) {
        if (numRows == 0) return Collections.emptyList();
        List<List<Integer>> list = new ArrayList<>();
        for (int i = 0; i < numRows; ++i) {
            List<Integer> sub = new ArrayList<>();
            for (int j = 0; j <= i; ++j) {
                if (j == 0 || j == i) {
                    sub.add(1);
                } else {
                    List<Integer> upSub = list.get(i - 1);
                    sub.add(upSub.get(j - 1) + upSub.get(j));
                }
            }
            list.add(sub);
        }
        return list;
    }
}
```


## 结语

如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-java-leetcode][ajl]



[title]: https://leetcode.com/problems/pascals-triangle
[ajl]: https://github.com/Blankj/awesome-java-leetcode