hdu 四边形优化dp

///题目大意：给定一个长度为n的序列，至多将序列分成m段，///每段序列都有权值,权值为序列内两个数两两相乘之和。///m<=n<=1000.#include<iostream>#include<cstring>#include<cstdio>#include<algorithm>using namespace std;const int maxn=1002;int INF=1<<30;int s[maxn][maxn],sum[maxn],ans,dp[maxn][maxn],pre[maxn][maxn];int n,m,a[maxn];void init(){    int i,j;    for(i=1;i<=n;++i)    for(j=1;j<=n;++j)        if (j<i) s[i][j]=0;        else s[i][j]=s[i][j-1]+a[j]*(sum[j-1]-sum[i-1]);    for(i=0;i<=n;++i)    {        dp[0][i]=s[1][i];        pre[0][i]=0,pre[i][n+1]=n;    }}int main(){  // freopen("//media/学习/ACM/input.txt","r",stdin);    while(scanf("%d%d",&n,&m),(n||m))    {        int i,j,k;        for(sum[0]=0,i=1;i<=n;i++)        {            scanf("%d",&a[i]);            sum[i]=sum[i-1]+a[i];        }        init();        for(i=1;i<=m;i++)        {            for(j=n;j>=i+1;j--)            {                dp[i][j]=INF;                for(k=pre[i-1][j-1];k<=pre[i][j+1];k++)                ///前导向，pre[i-1][j-1] 表示i-1次切断，到j-1位置的前导                {                    if(dp[i][j]>dp[i-1][k]+s[k+1][j])                    {                        dp[i][j]=dp[i-1][k]+s[k+1][j];                        pre[i][j]=k;                    }                }            }        }        printf("%d\n",dp[m][n]);    }    return 0;}