YACS2022年6月月赛甲组

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 1; i <= (n); ++i)

using std::cin;
using std::cout;
using std::multiset;
using ll = long long;

struct Node {
    ll x, h;
    int type;
    bool operator<(const Node &o) const {
        return x < o.x;
    }
} a[600005];

int main() {
    int n;
    cin >> n;
    
    rep(i, n) {
        int s, t, h;
        cin >> s >> t >> h;
        a[i*2-1] = {s, h, 0}; // 0 表示左边界
        a[i*2] = {t, h, 1}; // 1 表示右边界
    }
    
    int n2 = n*2;
    std::sort(a+1, a+n2+1);
    
    ll ans = 0;
    ll last = 0; // 扫描线上一次扫过的矩形高度的位置
    multiset<ll> st; // 维护当前存活着的的矩形高度
    st.insert(0);
    for (int i = 1; i <= n2;) {
        ll x = a[i].x;
        ans += *st.rbegin()*(a[i].x-last);
        last = a[i].x;
        while (i <= n2 and a[i].x == last) {
            if (a[i].type) st.erase(st.find(a[i].h));
            else st.insert(a[i].h);
            ++i;
        }
    }
    
    cout << ans << '\n';
    
    return 0;
}