Given an index 

k, return the 

k

^th row of the Pascal's triangle.

For example, given 

k = 3,

Return 

[1,3,3,1].

[      [1],     [1,1],    [1,2,1],   [1,3,3,1],  [1,4,6,4,1] ]

Note:

Could you optimize your algorithm to use only 

O(

k) extra space?

[解题报告]

滚动数组实现。注意Line11，要从后往前加，否则会产生冗余计算。

[Code]

1:    vector
    
      getRow(int rowIndex) {  2:      // Start typing your C/C++ solution below  3:      // DO NOT write int main() function  4:      vector
     
       result;  5:      result.resize(rowIndex+2);  6:      for(int i =0; i< rowIndex+2; i++)  7:        result[i] = 0;  8:      result[1]=1;  9:      for(int i =0; i< rowIndex; i++)  10:      {  11:        for(int j =rowIndex+1; j>0; j--)  12:        {  13:          result[j] = result[j-1] + result[j];  14:        }  15:      }  16:      result.erase(result.begin());  17:      return result;  18:    }