118. Pascal's Triangle

Easy

---

Given an integer numRows, return the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

Example 1:

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

Example 2:

Input: numRows = 1
Output: [[1]]

Constraints:

• 1 <= numRows <= 30

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        arr = [
            [1],
            [1,1],
            [1,2,1]
        ]
        if numRows <= 3:
            return arr[:numRows]
        for i in range(3, numRows):
            newRow = [1]
            for j in range(1, i):
                newRow.append(arr[i-1][j-1] + arr[i-1][j])
            newRow.append(1)
            arr.append(newRow)
        return arr