poj2184 Cow Exhibition

思路：
dp+滚动数组。
类似01背包。
实现：
 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 const int INF = 0x3f3f3f3f;
 7 const int t = 100000;
 8 int a[105], b[105], dp[2][200005], n, p, q;
 9 int solve(int n)
10 {
11     for (int i = 0; i < 2; i++)
12     {
13         for (int j = -t; j <= t; j++)
14         {
15             dp[i][j + t] = -INF;
16         }
17     }
18     for (int i = 0; i < 2; i++)
19         dp[i][a[i] + t] = b[i];
20     for (int i = 1; i < n; i++)
21     {
22         for (int j = -t; j <= t; j++)
23         {
24             dp[i & 1][j + t] = max(dp[(i - 1) & 1][j + t], dp[i & 1][j + t]);
25             if (j + t - a[i] < 0 || j + t - a[i] > 200000)
26                 continue;
27             dp[i & 1][j + t] = max(dp[i & 1][j + t], dp[(i - 1) & 1][j + t - a[i]] + b[i]);
28         }
29     }
30     int ans = -INF;
31     for (int j = 0; j <= t; j++)
32     {
33         ans = max(ans, dp[(n - 1) & 1][j + t] >= 0 ? j + dp[(n - 1) & 1][j + t] : -INF);
34     }
35     return ans;
36 }
37 
38 int main()
39 {
40     cin >> n;
41     int cnt = 0;
42     for (int i = 0; i < n; i++)
43     {
44         cin >> p >> q;
45         if (p < 0 && q < 0)
46             continue;
47         a[cnt] = p;
48         b[cnt++] = q;
49     }
50     int ans = solve(cnt);
51     if (ans <= -INF)
52         cout << "0" << endl;
53     else
54         cout << ans << endl;
55     return 0;
56 }