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?
思路：从后面往前加

class Solution {
public:
vector<int> getRow(int rowIndex) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.

vector<int> row;

for(int i=0; i<=rowIndex; i++){
for(int j=row.size()-1; j>0; j--){
row[j] = row[j] + row[j-1];
}
row.push_back(1);
}
return row;
}
};