关路灯

传送门

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define re register
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define P pair<int,int>
const int N=1e4;
const int mod=1e9+7;
void read(int &a)
{
    a=0;
    int d=1;
    char ch;
    while(ch=getchar(),ch>'9'||ch<'0')
        if(ch=='-')
            d=-1;
    a=ch-'0';
    while(ch=getchar(),ch>='0'&&ch<='9')
        a=a*10+ch-'0';
    a*=d;
}
void write(int x)
{
    if(x<0)
        putchar(45),x=-x;
    if(x>9)
        write(x/10);
    putchar(x%10+'0');
}
int f[55][55][2],a[55],sum[55],loc[55];
int main()
{
    int n,m;
    read(n);
    read(m);
    for(re int i=1;i<=n;i++)
    {
        read(loc[i]);
        read(a[i]);
    }
    for(re int i=1;i<=n;i++)
        sum[i]=a[i]+sum[i-1];
    memset(f,0x3f,sizeof(f));
    f[m][m][0]=0,f[m][m][1]=0;
    for(re int i=m;i<=n;i++)
        for(re int j=i-1;j>=1;j--)
        {
            f[j][i][0]=min(f[j+1][i][0]+(loc[j+1]-loc[j])*(sum[n]+sum[j]-sum[i]),f[j+1][i][1]+(loc[i]-loc[j])*(sum[n]+sum[j]-sum[i]));
            f[j][i][1]=min(f[j][i-1][1]+(loc[i]-loc[i-1])*(sum[n]+sum[j-1]-sum[i-1]),f[j][i-1][0]+(loc[i]-loc[j])*(sum[n]-sum[i-1]+sum[j-1]));
        }
    cout<<min(f[1][n][0],f[1][n][1]);
    return 0;
}