[LeetCode-119] Pascal's Triangle II

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?

 

和118基本没区别吧……

 

 1 class Solution {
 2 public:
 3     vector<int> getRow(int rowIndex) {
 4         // Start typing your C/C++ solution below
 5         // DO NOT write int main() function
 6         vector<int> vec_a(1, 1);
 7         vector<int> vec_b;
 8         vector<int> *vec_last = NULL, *vec_cur = NULL;
 9         bool flag = true;
10         if (0 == rowIndex) {
11             return vec_a;
12         }
13         for (int i = 1; i <= rowIndex; ++i) {
14             if (flag) {
15                 vec_last = &vec_a;
16                 vec_cur = &vec_b;
17             } else {
18                 vec_last = &vec_b;
19                 vec_cur = &vec_a;
20             }
21             vec_cur->clear();
22            
23             for (int j = 0; j <= i; ++j) {
24                 vec_cur->push_back((0 == j ? 0 : (*vec_last)[j - 1])
25                         + (i == j ? 0 : (*vec_last)[j]));
26             }
27             flag = !flag;
28         }
29         return *vec_cur;
30     }
31 };
View Code

 

posted on 2013-09-11 22:08  似溦若岚  阅读(132)  评论(0)    收藏  举报

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