LeetCode119 Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle. （Easy）

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

Note:
Could you optimize your algorithm to use only O(k) extra space?

分析：

上一题的followup，注意只能开O(k)的空间，实际上就是利用滚动数组的解法，每一行只与其上一行有关。

代码：

class Solution {
long long factorial(int n) {
    long long result = 1;
    for (int i = 1; i <= n; ++i) {
        result *= i;
    }
    return result;
}
public:
    vector<int> getRow(int rowIndex) {
        vector<int> result{1};
        vector<int> oldVec;
        for (int i = 2; i <= rowIndex + 1; ++i) {
            result.push_back(1);
            oldVec = result;
            for (int j = 1; j < i - 1; ++j) {
                result[j] = oldVec[j - 1] + oldVec[j];
            }
        }
        return result;
    }
};