如题。WA on #3,#18。

真看不出来了，奇怪。

#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;

#define ll long long
const int N = 100010;
int n; ll d, lft, ans;
ll v[N], a[N], sum[N];
vector<ll> st;
ll minn[N]; // DiZeng

ll getSum (int l, int r) {return sum[r - 1] - sum[l - 1];}


int main() {
    //freopen("road.in", "r", stdin);
    //freopen("road.out", "w", stdout);
    scanf("%d%lld", &n, &d);
    for (int i = 1; i < n; i++) scanf("%lld", &v[i]), sum[i] = sum[i - 1] + v[i];
    for (int i = 1; i <= n; i++) scanf("%lld", &a[i]);
    a[n] = 0;
    
    for (int i = n; i >= 1; i--) {
        while(!st.empty() && a[i] <= a[st.back()]) st.pop_back();
        st.size() ? minn[i] = st.back() : minn[i] = -1;
        st.push_back(i);
    }
    //minn[n - 1] = n;
    
    int sta = 1;
    while(sta != n) {
        int to = minn[sta]; ll need = getSum(sta, to);
        //printf("%d->%d ", sta, to);
        ll get = (need - lft) / d; if((need - lft) % d != 0) get++;
        //printf("get: %lld ", get);
        ans += get * a[sta];
        lft = get * d  + lft - need;
        //printf("lft: %lld\n", lft);
        sta = to;
    }
    
    printf("%lld", ans);
    return 0;
}