Leetcode: Pascal's Triangle II @Python

class Solution:
    # @return a list of integers
    def nCk(self,n,k):
        if n*k==0 or n<0 or k<0:
            return 1
        rst=1
        step=1
        for i in range(k+1,n+1):
            rst=rst*i//step
            step+=1
        return rst
    def getRow(self, rowIndex):
        return [self.nCk(rowIndex,i) for i in range(rowIndex+1)] if rowIndex>=0 else []