Leetcode Pascal's Triangle II

ven an index k, return the k^th row of the Pascal's triangle.

For example, given k = 3,
Return [1,3,3,1].

代码如下：

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

然而上面代码中的pre=temp这个复制操作是十分费时的，要想办法去掉从而提升效率，修改后的代码如下：

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> temp(rowIndex+1,1);

        for(int i=1;i<=rowIndex;i++)
        {
            int pre = temp[0];
            for(int j=1;j<i;j++)
            {
                int exchange = temp[j];
                temp[j] += pre;
                pre = exchange;              
            }

        }
        return temp;
    }
};