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?

相比之前, 有所改动

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int>ve1;
        ve1.push_back(1);
        if(rowIndex==0)
            return ve1;
        ve1.clear();  
        ve1.push_back(1);  
        ve1.push_back(1);  
        if(rowIndex==1)  
            return ve1;
        int i;
        int j;
        vector<int>ve2;
        for(i=2;i<=rowIndex;i++)
        {
            ve2.swap(ve1);
            ve1.clear();
            ve1.push_back(1);  
            for(j=0;j<i-1;j++)  
                ve1.push_back(ve2[j]+ve2[j+1]);  
            ve1.push_back(1);  
        }
        return ve1;
    }
};

用的space为两个vector<int>

ve1和ve2的长度为 k, k+1

O(space) = 2k+1