Submission #1175817

#	Time	Username	Problem	Language	Result	Execution time	Memory
1175817		InvMOD	Fancy Fence (CEOI20_fancyfence)	C++20	100 / 100	14 ms	2376 KiB

fancyfence

#include <bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define gcd __gcd
#define sz(v) (int) v.size()
#define pb push_back
#define pi pair<int,int>
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())
#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define REV(i, a, b) for(int i = (a); i >= (b); i--)
#define dbg(x) "[" #x " = " << (x) << "]"
///#define int long long

using ll = long long;
using ld = long double;
using ull = unsigned long long;

template<typename T> bool ckmx(T& a, const T& b){if(a < b) return a = b, true; return false;}
template<typename T> bool ckmn(T& a, const T& b){if(a > b) return a = b, true; return false;}

const int N = 2e5+5;
const ll MOD = 1e9+7;
const ll inv2 = 500000004;

int add(int x, int y){
    return (x + y < MOD ? x + y : x + y - MOD);
}

int sub(int x, int y){
    return add(x - y, MOD);
}

int mul(int x, int y){
    return (1ll * x * y) % MOD;
}

int bpow(int x, int y){
    int ans = 1;
    while(y){
        if(y & 1) ans = mul(ans, x);
        x = mul(x, x);
        y >>= 1;
    }
    return ans;
}

int sumN(int x){
    return mul(mul(x, add(x, 1)), inv2);
}


void solve()
{
    int n; cin >> n;

    vector<int> h(n + 1), w(n + 1);
    FOR(i, 1, n) cin >> h[i];
    FOR(i, 1, n) cin >> w[i];

    vector<int> pref(n + 1);
    FOR(i, 1, n) pref[i] = add(w[i], pref[i - 1]);

    vector<int> dp(n + 1); stack<int> st; st.push(0);

    int answer = 0;
    FOR(i, 1, n){
        while(h[i] <= h[st.top()]) st.pop();

        int rect_sum = mul(sub(pref[i - 1], pref[st.top()]), mul(w[i], sumN(h[i])));

        rect_sum = add(rect_sum, mul(sumN(w[i]), sumN(h[i])));
        answer = add(answer, rect_sum);
        answer = add(answer, mul(dp[st.top()], w[i]));

        dp[i] = mul(sub(pref[i], pref[st.top()]), sumN(h[i]));
        dp[i] = add(dp[i], dp[st.top()]);
        st.push(i);
    }

    cout << answer << "\n";
}

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    #define name "InvMOD"
    if(fopen(name".INP", "r")){
        freopen(name".INP","r",stdin);
        freopen(name".OUT","w",stdout);
    }

    int t = 1; //cin >> t;
    while(t--) solve();
    return 0;
}

Compilation message (stderr)

fancyfence.cpp: In function 'int main()':
fancyfence.cpp:94:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   94 |         freopen(name".INP","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
fancyfence.cpp:95:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   95 |         freopen(name".OUT","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 0
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 18 / 18
• Subtask 7: 27 / 27