119. Pascal's Triangle II (Graph; WFS)

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?

 

思路：从右往左遍历并填写三角形的图结构

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> a(rowIndex + );

        a[] = ;
        for(int i = ; i <= rowIndex; i++) //遍历行
            for(int j = i; j >= ; j--) //遍历行中的元素，第k行有k个元素。注意行中元素需要从右往左遍历，否则下一行填写的结果会覆盖上一行还未使用的元素
                if (j == i)
                    a[j] = a[j-];
                else if (j == )
                    a[j] = a[j];
                else
                    a[j] = a[j-] + a[j];

        return a;
    }
};