118. Pascal's Triangle

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,

Return

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

class Solution(object):
def generate(self, numRows):
List = []
if numRows <= 0 :
return List
List = [i for i in range(numRows+1)]
for i in range(numRows+1):
List[i] = []
if numRows == 1:
List[0].append(1)
List[1].extend([1,1])
else:
List[0].append(1)
List[1].extend([1,1])
for i in range(2,numRows+1):
cnt = len(List[i-1])
List[i].append(1)
for j in range(cnt-1):
List[i].append(List[i-1][j]+List[i-1][j+1])
List[i].append(1)
return List[:numRows]