#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=5005;
int f[N],t[N],c[N];
int main(){
    int n,s;
    scanf("%d%d",&n,&s);
    for(int i=1;i<=n;i++){
        scanf("%d%d",&t[i],&c[i]);
        t[i]+=t[i-1],c[i]+=c[i-1];
    }
    memset(f,0x3f,sizeof f);
    f[0]=0;
    for(int i=1;i<=n;i++)
        for(int j=0;j<i;j++)
            f[i]=min(f[i],f[j]+t[i]*(c[i]-c[j])+s*(c[n]-c[j]));
    printf("%d",f[n]);
    return 0;
}

老师的错了~~ $hhh$

C++ :

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 5005;
int f[N],t[N],c[N];
int main(){
    int n,s;
    scanf("%d%d",&n,&s);
    for(int i = 1;i <= n;i++){
        scanf("%d%d",&t[i],&c[i]);
        t[i] += t[i-1],c[i] += c[i-1];
    }
    memset(f,0x3f,sizeof f);
    f[0] = 0;
    for(int i = 1;i <= n;i++){
        for(int j = 0;j < i;j++){
            f[i] = min(f[i],f[j] + t[i] * (c[i] - c[j]) + s * (c[n] - c[j]));
        }
    }
    printf("%d\n",f[n]);
    return 0;
}