luogu 1220 关路灯 区间dp

Code:

#include <bits/stdc++.h>
#define ll long long
#define N 1003
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
void getmin(ll &a,ll b)
{
    if(b<a) a=b;
}
ll x[N],sum[N],f[N][N][3],val[N];
int main()
{
    // setIO("input");
    int n,pos,i,j,len;
    scanf("%d%d",&n,&pos);
    for(i=1;i<=n;++i) scanf("%lld%lld",&x[i],&val[i]);
    for(i=1;i<=n;++i) sum[i]=sum[i-1]+val[i];
    memset(f,0x3f,sizeof(f));
    f[pos][pos][0]=f[pos][pos][1]=0;
    for(len=2;len<=n;++len)
    {
        int l,r;
        for(l=1;l+len-1<=n;++l)
        {
            r=l+len-1;
            getmin(f[l][r][0], f[l+1][r][0]+(x[l+1]-x[l])*(sum[n]-sum[r]+sum[l]));
            getmin(f[l][r][0], f[l+1][r][1]+(x[r]-x[l])*(sum[n]-sum[r]+sum[l]));
            getmin(f[l][r][1], f[l][r-1][1]+(x[r]-x[r-1])*(sum[n]-sum[r-1]+sum[l-1]));
            getmin(f[l][r][1], f[l][r-1][0]+(x[r]-x[l])*(sum[n]-sum[r-1]+sum[l-1]));
        }
    }
    printf("%lld\n",min(f[1][n][0], f[1][n][1]));
    return 0;
}