118. Pascal's Triangle

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|1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

Input: numRows = 1
Output: 1

def generate(self, numRows: int) -> List[List[int]]:
	ls = []
	if numRows == 0:
		return []
	if numRows == 1:
		return [[1]]
	ls = [[1], [1,1]]
	for i in range(2,numRows):
		ls.append([1])
		j = 0
		while j + 1 < len(ls[-2]):
			ls[-1].append(ls[-2][j] + ls[-2][j+1])
			j += 1
		ls[-1].append(1)
	return ls