51Nod 1022（四边形优化dp）

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAXN=2004,INF=0x3f3f3f3f;
int n,a[MAXN],dp[MAXN][MAXN],s[MAXN][MAXN],sum[MAXN][MAXN];
int main() {
while (~scanf("%d",&n)) {
memset(sum,0,sizeof(sum));
for (int i=1;i<=n;++i) scanf("%d",&a[i]),a[n+i]=a[i];
for (int i=1;i<=(n<<1);++i) dp[i][i]=0,s[i][i]=i;
for (int i=1;i<=(n<<1);++i)
for (int j=i;j<=min(i+n,n<<1);++j)
sum[i][j]=sum[i][j-1]+a[j];
for (int len=2;len<=n;++len)
for (int i=1;i+len-1<=(n<<1);++i) {
int j=i+len-1;
dp[i][j]=INF;
for (int k=s[i][j-1];k<=s[i+1][j];++k) {
if (dp[i][j]>dp[i][k]+dp[k+1][j]+sum[i][j])
dp[i][j]=dp[i][k]+dp[k+1][j]+sum[i][j],s[i][j]=k;
}
}
int ans=INF;
for (int i=1;i<=n;++i)
ans=min(ans,dp[i][i+n-1]);
printf("%d\n",ans);
}
return 0;
}