【64.22】【E】【leetcode】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?

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利用杨辉三角的公式，算

第n行的m个数可表示为C(n-1,m-1)

class Solution(object):
    def cal(self,a,b):
        res = 1
        for i in range(0,b):
            res *= (a-i)
        for i in range(1,b+1):
            res /= i
        return res
    def getRow(self, rowIndex):
       
        r = rowIndex
       
        res = [0]*(r+1)
        #temp = [0]*(r+1)
       
        for i in range(0,r+1):
            res[i] = self.cal(r,i)
           
        #print res
        return res
       
        """
        :type rowIndex: int
        :rtype: List[int]
        """