This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include "../Library/debug.h"
#else
#define dbg(x...)
// #define cin fin
// #define cout fout
// const string FILE_NAME = ""; ifstream fin(FILE_NAME + ".in"); ofstream fout(FILE_NAME + ".out");
#endif
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) for (int i = 0; i < (a); ++i)
#define FORd(i, a, b) for (int i = (b) - 1; i >= (a); --i)
#define F0Rd(i, a) for (int i = (a) - 1; i >= 0; --i)
#define trav(a, x) for (auto& a : x)
#define f first
#define s second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
const char nl = '\n';
const int INF = 1e9;
const ll MOD = 1e9 + 7;
const int mxN = 1e6 + 1;
ll mul(ll a, ll b){
return (ll) a * b % MOD;
}
const ll INV_TWO = (MOD + 1) / 2;
ll half(ll a){
return mul(a, INV_TWO);
}
void add_self(ll& a, ll b){
a += b;
if(a >= MOD)
a -= MOD;
}
ll f(ll a){
return half(mul(a, a + 1));
}
void solve(){
int n;
cin >> n;
vl h(n + 1), w(n + 1);
F0R(i, n)
cin >> h[i];
F0R(i, n)
cin >> w[i];
h[n] = 0;
w[n] = 0;
// h, totalw;
stack<array<ll, 2>> st;
ll ans = 0;
FOR(i, 0, n + 1){
ll w_left = 0;
while(!st.empty() && st.top()[0] >= h[i]){
w_left += st.top()[1];
add_self(ans, mul(f(st.top()[0]), f(w_left)));
add_self(ans, -mul(f(st.top()[0]), f(w_left - st.top()[1])));
st.pop();
}
dbg(i, w_left, h[i], w[i]);
dbg(ans);
if(w_left != 0){
add_self(ans, -mul(f(h[i]), f(w_left)));
}
dbg(ans);
st.push({h[i], w[i] + w_left});
}
cout << ans << nl;
}
int32_t main(){
ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int TC = 1;
/* cin >> TC; */
while(TC--){
solve();
}
return 0;
}
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