Submission #915210

#	Time	Username	Problem	Language	Result	Execution time	Memory
915210		vjudge1	Roller Coaster Railroad (IOI16_railroad)	C++17	100 / 100	184 ms	23336 KiB

railroad

#include "railroad.h"

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

struct dsu {
        vector<int> p;
        dsu(int n) : p(n, -1) {}
        bool unite(int u, int v) {
                if ((u = root(u)) == (v = root(v))) return false;
                if (p[u] > p[v]) swap(u, v);
                p[u] += p[v];
                p[v] = u;
                return true;
        }
        bool same(int u, int v) { return root(u) == root(v); }
        int root(int u) { return p[u] < 0 ? u : p[u] = root(p[u]); }
};

long long plan_roller_coaster(std::vector<int> s, std::vector<int> t) {
        int n = (int)s.size() + 1;
        s.emplace_back(1e9);
        t.emplace_back(1);

        vector<int> point;
        for (int i = 0; i < n; i++) {
                point.push_back(s[i]);
                point.push_back(t[i]);
        }
        sort(point.begin(), point.end());
        point.erase(unique(point.begin(), point.end()), point.end());
        vector<int> a(n), b(n);
        for (int i = 0; i < n; i++) {
                a[i] = lower_bound(point.begin(), point.end(), s[i]) - point.begin();
                b[i] = lower_bound(point.begin(), point.end(), t[i]) - point.begin();
        }
        int m = point.size();
        vector<int> pref(m);
        for (int i = 0; i < n; i++) pref[a[i]]++, pref[b[i]]--;
        for (int i = 1; i < m; i++) pref[i] += pref[i - 1];

        int64_t res = 0;
        dsu d(m);
        for (int i = 0; i + 1 < m; i++) {
                res += 1ll * max(0, pref[i]) * (point[i + 1] - point[i]);
                if (pref[i] != 0) d.unite(i, i + 1);
        }

        for (int i = 0; i < n; i++) d.unite(a[i], b[i]);
        vector<tuple<int, int, int>> edges;
        for (int i = 0; i + 1 < m; i++) {
                edges.emplace_back(point[i + 1] - point[i], i, i + 1);
        }

        sort(edges.begin(), edges.end());
        for (auto [w, u, v] : edges) {
                if (d.unite(u, v)) res += w;
        }

        return res;
}

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