제출 #1319663

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1319663		chithanhnguyen	Fancy Fence (CEOI20_fancyfence)	C++20	100 / 100	24 ms	5256 KiB

fancyfence

/*
Author: Nguyen Chi Thanh - High School for the Gifted - VNU.HCM (i2528)
*/
#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1ll << (x)))

#define debug(a, l, r) for (int _i = (l); _i <= (r); ++_i) cout << (a)[_i] << ' '; cout << '\n';

const int MAXN = 1e5 + 5;
const int MOD  = 1e9 + 7;
int n, h[MAXN], w[MAXN];

void init() {
    cin >> n;
    for (int i = 1; i <= n; ++i) cin >> h[i];
    for (int i = 1; i <= n; ++i) cin >> w[i];
}

// x * (x - 1) / 2
int C2 (int x) {
    int f1 = x, f2 = x - 1;
    if (f1 % 2 == 0) f1 /= 2;
    else f2 /= 2;
    f1 %= MOD; f2 %= MOD;
    return f1 * f2 % MOD;
}

void add(int &x, int y) {x = (x + y) % MOD;}
void sub(int &x, int y) {x = ((x - y) % MOD + MOD) % MOD;}

int cnt_sub_rects(int x, int y) {
    return C2(x + 1) * C2(y + 1) % MOD;
}

namespace subtask6 {
    bool check() {return n <= 1000;}

    const int INF = 1e9 + 7;
    
    void solve() {
        int res = 0;

        for (int i = 1; i <= n; ++i) {
            int minhi = INF, len = 0;

            for (int j = i; j <= n; ++j) {
                minhi = min(minhi, h[j]);
                len += w[i];

                if (i == j) 
                    add(res, cnt_sub_rects(minhi, len));
                else {
                    int contrib = cnt_sub_rects(minhi, len);
                    sub(contrib, cnt_sub_rects(minhi, len - w[i]));
                    sub(contrib, cnt_sub_rects(minhi, len - w[j]));
                    add(contrib, cnt_sub_rects(minhi, len - w[i] - w[j]));
                    add(res, contrib);
                }
            }
        }

        cout << res;
    }
}

namespace full {
    int left[MAXN], right[MAXN], pref[MAXN];

    void prepare() {
        vector<int> st; // Stack-based vector
        for (int i = 1; i <= n; ++i) {
            while (!st.empty() && h[st.back()] >= h[i]) st.pop_back();
    
            if (!st.empty()) left[i] = st.back();
            else left[i] = 0;
    
            st.push_back(i);
        }

        st.clear();

        for (int i = n; i >= 1; --i) {
            while (!st.empty() && h[st.back()] > h[i]) st.pop_back();
    
            if (!st.empty()) right[i] = st.back();
            else right[i] = n + 1;
    
            st.push_back(i);
        }

        // Build prefix sum
        for (int i = 1; i <= n; ++i)
            pref[i] = pref[i - 1] + w[i];
    }

    int get_sum(int l, int r) {
        return pref[r] - pref[l - 1];
    }

    void solve() {
        prepare();

        int res = 0;
        for (int i = 1; i <= n; ++i) {
            int l = left[i] + 1, r = right[i] - 1;
            int total_len = get_sum(l, r);
            int left_len = pref[i - 1] - pref[l - 1];
            int right_len = pref[r] - pref[i];

            int contrib = cnt_sub_rects(total_len, h[i]);
            sub(contrib, cnt_sub_rects(left_len, h[i]));
            sub(contrib, cnt_sub_rects(right_len, h[i]));

            add(res, contrib);
        }

        cout << res;
    }
}

signed main() {
    #ifdef NCTHANH
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    #endif
    ios_base::sync_with_stdio(0);
    cin.tie(nullptr); cout.tie(nullptr);

    init();
    // if (subtask6::check()) return subtask6::solve(), 0;
    full::solve();

    // cout << cnt_sub_rects(1, 3) - cnt_sub_rects(1, 0) - cnt_sub_rects(1, 2) << '\n';
    // cout << cnt_sub_rects(2, 2);

    return 0;
}

• 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