Leetcode with Python -> Array

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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 +

 

Leetcode with Python -> Array