[LeetCode-119] Pascal's Triangle II

Pascal's Triangle II

Given an index k, return the k^th 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?

 

和118基本没区别吧……

 

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> vec_a(1, 1);
        vector<int> vec_b;
        vector<int> *vec_last = NULL, *vec_cur = NULL;
        bool flag = true;
        if (0 == rowIndex) {
            return vec_a;
        }
        for (int i = 1; i <= rowIndex; ++i) {
            if (flag) {
                vec_last = &vec_a;
                vec_cur = &vec_b;
            } else {
                vec_last = &vec_b;
                vec_cur = &vec_a;
            }
            vec_cur->clear();
           
            for (int j = 0; j <= i; ++j) {
                vec_cur->push_back((0 == j ? 0 : (*vec_last)[j - 1])
                        + (i == j ? 0 : (*vec_last)[j]));
            }
            flag = !flag;
        }
        return *vec_cur;
    }
};