Pascal's Triangle II

Given an index k, return the kth 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:

最开始的想法是用两个vector依次记录当前行和上一行的结果。但是要求用k的空间,所以使用一个vector,每次从后往前r[j] = r[j] + r[j-1]即可。

代码:

 1     vector<int> getRow(int rowIndex) {
 2         // IMPORTANT: Please reset any member data you declared, as
 3         // the same Solution instance will be reused for each test case.
 4         vector<int> result(rowIndex+1,0);
 5         result[0] = 1;
 6         int i, j;
 7         for(i = 1;  i <= rowIndex; i++){
 8             for(j = i; j > 0; j--){
 9                 result[j] = result[j] + result[j-1];
10             }
11         }
12         return result;
13     }

 

posted on 2013-11-06 10:32  waruzhi  阅读(133)  评论(0编辑  收藏  举报

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