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?

只用O（k）的额外空间，求第K行帕斯卡三角形的数

C++(0ms):

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> res(rowIndex+1,0) ;
        res[0] = 1 ;
        for(int i = 1 ; i < rowIndex+1 ; i++){
            for(int j = i ; j >=1 ; j--){
                res[j] += res[j-1] ;
            }
        }
        return res ;
    }
};

java(2ms):

class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> list = new ArrayList<Integer>(rowIndex+1) ;
        if (rowIndex < 0)
            return list ;
        
        for(int i = 0 ; i <= rowIndex ; i++){
            list.add(1) ;
            for(int j = i-1 ; j >= 1 ; j--){
                list.set(j , list.get(j) + list.get(j-1)) ;
            }
        }
        return list ;
    }
}