leetcode-pascal triangle I&&II

对于第2个pascal triangle,通过观察可以发现，其实只需要2个额外的变量来记录，于是就设了个tmp数组。
整体有点DP问题中的滚动数组的感觉。
 1 #include <vector>
 2 #include <iostream>
 3 using namespace std;
 4 
 5 class Solution {
 6 public:
 7     vector<vector<int> > generate(int numRows) {
 8         vector<vector<int>> res;
 9         if (numRows == 0) return res;
10         for (int i = 0; i < numRows; i++)
11         {
12             vector<int> v; v.clear();
13             for (int j = 0; j <= i; j++)
14             {
15                 if (j == 0 || j == i) v.push_back(1);
16                 if (i>0 && j > 0 && j < i)
17                 {
18                     v.push_back(res[i - 1][j] + res[i - 1][j - 1]);
19                 }
20             }
21             res.push_back(v);
22         }
23         return res;///////////忘了返回了，一直找不出错来。
24     }
25     vector<int> getRow(int rowIndex) {
26         vector<int> res(rowIndex+1,0);
27         vector<int> tmp(2,0);
28         //if (rowIndex == 0) return vector<int>(1,1);
29         for (int i = 0; i <= rowIndex; i++)
30         {
31             tmp[0] = 1; tmp[1] = 1;//别放错位置。之前放到内层的for里了。
32             for (int j = 0; j <= i; j++)
33             {
34                 if (j == 0 || j == i)
35                     res[j] = 1;
36                 if (j>0 && j < i)
37                 {
38                     if (j % 2 == 0)
39                         tmp[0] = res[j];
40                     else if (j % 2 == 1)
41                         tmp[1] = res[j];
42                     res[j] += tmp[1-j%2];
43                 }
44             }
45         }
46         return res;
47     }
48 };
49 
50 void printVV(vector<vector<int>> vv)
51 {
52     for (int i = 0; i < vv.size(); i++)
53     {
54         for (int j = 0; j < vv[i].size(); j++)
55         {
56             cout << vv[i][j] << " ";
57         }
58         cout << endl;
59     }
60 }
61 int main()
62 {
63     Solution s;
64     //vector<vector<int>> vv = s.generate(3);
65     vector<int> v = s.getRow(0);
66     for (int i = 0; i < v.size(); i++)
67     {
68         cout << v[i] << " ";
69     }
70     //printVV(vv);
71     return 0;
72 }