Submission #426368

#	Time	Username	Problem	Language	Result	Execution time	Memory
426368		timmyfeng	Roller Coaster Railroad (IOI16_railroad)	C++17	100 / 100	1888 ms	59676 KiB

railroad

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

unordered_map<int, int> par;

int find(int u) {
    if (par.count(u) > 0) {
        return par[u] = find(par[u]);
    } else {
        return u;
    }
}

bool unite(int u, int v) {
    u = find(u), v = find(v);
    if (u != v) {
        par[u] = v;
        return true;
    }
    return false;
}
 
long long plan_roller_coaster(vector<int> s, vector<int> t) {
    s.push_back(INT_MAX), t.push_back(1);
    int n = s.size();

    map<int, int> events;
    for (int i = 0; i < n; ++i) {
        unite(s[i], t[i]);
        ++events[s[i]];
        --events[t[i]];
    }

    long long ans = 0;
    int prv = 1, balance = 0;
    vector<array<int, 3>> edges;
    for (auto [x, d] : events) {
        if (balance != 0) {
            ans += (long long) (x - prv) * max(0, balance);
            unite(prv, x);
        }

        edges.push_back({x - prv, prv, x});
        balance += d;
        prv = x;
    }
    sort(edges.begin(), edges.end());

    for (auto [w, u, v] : edges) {
        if (unite(u, v)) {
            ans += w;
        }
    }

    return ans;
}

• Subtask 1: 11 / 11
• Subtask 2: 23 / 23
• Subtask 3: 30 / 30
• Subtask 4: 36 / 36