AC code

#include<bits/stdc++.h>

using namespace std;

int main()
{
    int n,m;
    int pi[100005];
    int ai[100005];
    int bi[100005];
    int ci[100005];
    int change[100005];
    long long ans = 0;

    memset(pi,0,sizeof(pi));
    memset(ai,0,sizeof(ai));
    memset(bi,0,sizeof(bi));
    memset(ci,0,sizeof(ci));

    cin>>n>>m;
    for(int i = 1;i < n;i++)
    {
        change[i] = 0;
    }
    change[0] = 0;
    for(int i = 1;i <= m;i++)
    {
        cin>>pi[i];
    }
    for(int i = 1;i < n;i++)
    {
        cin>>ai[i]>>bi[i]>>ci[i];
    }
    change[0] = 0;

    for(int i = 1;i <= m - 1;i++)
    {
        int l = min(pi[i], pi[i+1]);
        int r = max(pi[i], pi[i+1]);

        change[l]++;
        change[r]--;
    }

    for(int i = 1;i < n;i++)
    {
        change[i] = change[i-1] + change[i];
        ans += min((long long int)ai[i] * change[i],(long long int)bi[i] * change[i] + ci[i]);
    }
    cout<<ans<<endl;
    return 0;
}