Submission #618276

#	Time	Username	Problem	Language	Result	Execution time	Memory
618276		Zanite	Roller Coaster Railroad (IOI16_railroad)	C++17	100 / 100	295 ms	35760 KiB

railroad

#include "railroad.h"

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

using ll	= long long;
using pll	= pair<ll, ll>;
using Edge	= pair<ll, pll>;

#define fi	first
#define se	second

const ll maxN	= 17;
const ll INF	= 1e18;

ll n;
vector<ll> compress;
vector<ll> cs, ct;

struct DSU {
	vector<ll> par, sz;
	
	DSU(ll n) {
		par = sz = vector<ll>(n+1, 1);
		iota(par.begin(), par.end(), 0);
	}

	ll rep(ll x) {
		return ((x == par[x]) ? (x) : (par[x] = rep(par[x])));
	}

	bool check(ll x, ll y) {
		return (rep(x) == rep(y));
	}

	void join(ll x, ll y) {
		ll a = rep(x), b = rep(y);
		if (a == b) return;
		if (sz[a] < sz[b]) {swap(a, b);}
		par[b] = a;
		sz[a] += sz[b];
	}
};

ll plan_roller_coaster(vector<int> s, vector<int> t) {
	n = s.size();
	
	for (auto i : s) {compress.push_back(i);}
	for (auto i : t) {compress.push_back(i);}
	compress.push_back(0);
	compress.push_back(INF);
	sort(compress.begin(), compress.end());
	compress.erase(unique(compress.begin(), compress.end()), compress.end());

	for (auto i : s) {
		cs.push_back(lower_bound(compress.begin(), compress.end(), i) - compress.begin());
	}
	for (auto i : t) {
		ct.push_back(lower_bound(compress.begin(), compress.end(), i) - compress.begin());
	}

	ll CS = compress.size();
	DSU D = DSU(CS);

	//for (auto i : compress) cout << i << ' '; cout << '\n';

	// edges for MST
	vector<Edge> edges;
	for (ll i = 1; i < compress.size(); i++) {
		edges.push_back({compress[i] - compress[i-1], {i-1, i}});
	}

	vector<ll> lines(CS, 0);
	// right line = 1, left line = -1
	for (ll i = 0; i < n; i++) {
		D.join(cs[i], ct[i]);

		//cout << i << ' ' << cs[i] << ' ' << ct[i] << '\n';

		if (s[i] < t[i]) {
			// right line
			lines[cs[i]]++;
			lines[ct[i]]--;
		} else {
			// left line
			lines[ct[i]]--;
			lines[cs[i]]++;
		}
	}
	lines[0]--;

	//for (auto i : lines) cout << i << ' '; cout << '\n';
	
	ll run = 0, ans = 0;
	for (ll i = 0; i < CS-1; i++) {
		run += lines[i];
		//cout << run << ' ';

		if (run > 0) {
			// more right lines than left lines
			ans += 1ll * run * (compress[i+1] - compress[i]);
			D.join(i, i+1);

		} else if (run < 0) {
			// more left lines than right lines
			D.join(i, i+1);
		}
	}
	//cout << '\n';

	// make the graph connected via Kruskal
	sort(edges.begin(), edges.end());
	for (auto &[w, p] : edges) {
		if (D.check(p.fi, p.se)) continue;
		ans += compress[p.se] - compress[p.fi];
		D.join(p.fi, p.se);
	}

	return ans;
}

#ifdef Zanite
int main() {
    int n;
    assert(1 == scanf("%d", &n));
    std::vector<int> s(n), t(n);
    for (int i = 0; i < n; ++i)
        assert(2 == scanf("%d%d", &s[i], &t[i]));
    long long ans = plan_roller_coaster(s, t);
    printf("%lld\n", ans);
    return 0;
}
#endif

Compilation message (stderr)

railroad.cpp: In function 'll plan_roller_coaster(std::vector<int>, std::vector<int>)':
railroad.cpp:69:19: warning: comparison of integer expressions of different signedness: 'll' {aka 'long long int'} and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   69 |  for (ll i = 1; i < compress.size(); i++) {
      |                 ~~^~~~~~~~~~~~~~~~~

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