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):
"""
:type numRows: int
:rtype: List[List[int]]
"""
res = [[1]]
for i in range(1,numRows):
res += [map(lambda x, y:x+y,res[-1]+[0],[0]+res[-1])]
return res[:numRows]
# [[1]]+[0] -> [[1],0]
# [[1]]+[0,1] ->[[1],0,1]
# [[1]]+[[0]] -> [[1],[0]]
# [[1]]+0 -> error
# the code is elegant, but slow. the reason lies in the fact that it generates too much list while looping
# be careful when numRows is 0, res[:numRows] will return [] when it happens
119. Pascal‘s Triangle II
Given an index k, return the kth row of the Pascal‘s triangle.
For example, given k = 3,
Return [1,3,3,1].
Note:
Could you optimize your algorithm to use only O(k) extra space?
class Solution(object):
def getRow(self, rowIndex):
"""
:type rowIndex: int
:rtype: List[int]
"""
res = [1]
for i in range(0, rowIndex):
res = [ i+j for i,j in zip(res + [0], [0] + res)]
return res
# list can‘t be added elementwisely with +
