HDU 3506 DP 四边形不等式优化 Monkey Party

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 
 6 using namespace std;
 7 
 8 const int maxn = 2000 + 10;
 9 const int INF = 0x3f3f3f3f;
10 
11 int n;
12 
13 int a[maxn], sum[maxn];
14 int d[maxn][maxn], s[maxn][maxn];
15 
16 int main()
17 {
18     while(scanf("%d", &n) == 1 && n)
19     {
20         for(int i = 1; i <= n; i++) scanf("%d", a + i);
21         for(int i = n + 1; i < n * 2; i++) a[i] = a[i - n];
22         for(int i = 1; i < n * 2; i++) sum[i] = sum[i - 1] + a[i];
23 
24         for(int i = 1; i + 1 < n * 2; i++)
25         {
26             s[i][i+1] = i;
27             d[i][i+1] = a[i] + a[i+1];
28         }
29 
30         for(int l = 3; l <= n; l++)
31         {
32             for(int i = 1; i + l - 1 < n * 2; i++)
33             {
34                 int j = i + l - 1;
35                 d[i][j] = INF;
36                 for(int k = s[i][j-1]; k <= s[i+1][j]; k++)
37                 {
38                     int t = d[i][k] + d[k+1][j] + sum[j] - sum[i-1];
39                     if(t < d[i][j])
40                     {
41                         d[i][j] = t;
42                         s[i][j] = k;
43                     }
44                 }
45             }
46         }
47 
48         int ans = INF;
49         for(int i = 1; i <= n; i++) ans = min(ans, d[i][i+n-1]);
50         printf("%d\n", ans);
51     }
52 
53     return 0;
54 }