Given an index k, return the kth row of the Pascal’s triangle.
Pascal’s triangle : To generate A[C] in row R, sum up A’[C] and A’[C-1] from previous row R - 1.
Input : k = 3 Return : [1,3,3,1]
NOTE : k is 0 based. k = 0, corresponds to the row .
Note:Could you optimize your algorithm to use only O(k) extra space?