#include <bits/stdc++.h> using namespace std; #define int long long #define FOR(I, L, R) for(int I(L) ; I <= (int)R ; ++I) #define FOD(I, R, L) for(int I(R) ; I >= (int)L ; --I) #define FOA(I, A) for(auto &I : A) #define print(A,L,R) FOR(OK, L, R){if(A[OK]<=-oo / 10||A[OK]>=oo)cout<<"- ";else cout<<A[OK]<<' ';}cout<<'\n'; #define prints(A) FOA(OK, A){cout<<OK<<' ';}cout << '\n'; #define printz(A,L,R) FOR(OK, 1, L){FOR(KO, 1, R){if(A[OK][KO]>-oo&&A[OK][KO]<oo)cout<<A[OK][KO]<<' ';else cout << "- ";} cout << '\n';}cout << '\n'; #define fs first #define sd second #define ii pair<int,int> #define iii pair<int, ii> #define all(A) A.begin(), A.end() #define quickly ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); #define FILE "FILE" const int N = 5000 + 5; const int mod = 1e9 + 7; const int inv = (mod + 1) / 2; const int oo = 1e18; struct Modint{ int x; Modint(){x = 0;} Modint(int _x){ x = (_x % mod + mod) % mod; } inline Modint operator + (const Modint &other) const{ return (x + other.x) % mod; } inline Modint operator - (const Modint &other) const{ return (x - other.x + mod) % mod; } inline Modint operator * (const Modint &other) const{ return (1LL * x * other.x) % mod; } inline void operator += (const Modint &other){ *this = *this + other; } inline void operator -= (const Modint &other){ *this = *this - other; } inline void operator *= (const Modint &other){ *this = *this * other; } friend ostream& operator << (ostream& os, const Modint &t){ return os << t.x; } }; int n; int h[N], w[N], pre[N]; int L[N], R[N]; stack<int> st; Modint f(Modint x){ return x * (x + 1) * inv; } signed main(){ quickly if(fopen(FILE".inp", "r")){ freopen(FILE".inp", "r", stdin); freopen(FILE".out", "w", stdout); } cin >> n; FOR(i, 1, n){ cin >> h[i]; } FOR(i, 1, n){ cin >> w[i]; pre[i] = pre[i - 1] + w[i]; } FOR(i, 1, n){ while(!st.empty() && h[st.top()] >= h[i]){ st.pop(); } if(!st.empty()) L[i] = st.top(); st.push(i); } st = stack<int>(); FOD(i, n, 1){ while(!st.empty() && h[st.top()] > h[i]){ st.pop(); } R[i] = n + 1; if(!st.empty()) R[i] = st.top(); st.push(i); } Modint ans = 0; FOR(i, 1, n){ int x = h[i]; int y = w[i]; int l = L[i] + 1, r = R[i] - 1; int k = pre[r] - pre[l - 1]; int u = pre[i - 1] - pre[l - 1]; int v = pre[r] - pre[i]; ans += f(x) * u * v + f(x) * f(y) + f(x) * y * (u + v); } cout << ans; }

fancyfence.cpp: In function 'int main()':
fancyfence.cpp:56:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   56 |                 freopen(FILE".inp", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
fancyfence.cpp:57:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   57 |                 freopen(FILE".out", "w", stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~