Submission #284342

#	Time	Username	Problem	Language	Result	Execution time	Memory
284342		user202729	Roller Coaster Railroad (IOI16_railroad)	C++17	100 / 100	257 ms	18552 KiB

railroad

// moreflags=grader.cpp
#include "railroad.h"
// 16
// is this cheating?...
// again, I should have solved this problem earlier.

#include<algorithm>
#include<numeric>
#if not LOCAL
#define NDEBUG 1
#endif
#include<cassert>

struct Dsu{
	std::vector<int> data;
	Dsu(int number): data(number){
		while(number--) data[number]=number;
	}
	void join(int first, int sec){
		first=root(first); sec=root(sec);
		data[first]=sec;
	}
	int root(int node){
		return data[node]!=node? data[node]=root(data[node]): node;
	}
};

long long plan_roller_coaster(std::vector<int> s, std::vector<int> t) {
	std::vector<int> values; values.reserve(s.size()+t.size());
	for(auto it: s) values.push_back(it);
	for(auto it: t) values.push_back(it);

	std::sort(begin(values), end(values));
	values.resize(std::unique(begin(values), end(values))-values.begin());

	std::vector<int> degree(values.size());
	Dsu dsu((int)values.size());
	for(int i=0; i<(int)s.size(); ++i){
		auto const a=int(std::lower_bound(begin(values), end(values), s[i])-begin(values));
		auto const b=int(std::lower_bound(begin(values), end(values), t[i])-begin(values));
		degree[a]++;
		degree[b]--;
		dsu.join(a, b);
	}
	degree[0]--; // add a huge edge downward
	dsu.join(0, (int)values.size()-1);

	std::partial_sum(begin(degree), end(degree), degree.begin());
	degree.pop_back();

	struct Edge{int len, first, sec;};
	std::vector<Edge> pending;

	int64_t result{};
	for(int index=0; index<(int)degree.size(); ++index){
		auto const edgeLen=values[index+1]-values[index];
		if(degree[index]>0)
			result+=int64_t(edgeLen)*degree[index];
		if(degree[index]!=0)
			dsu.join(index, index+1);
		else if(dsu.root(index)!=dsu.root(index+1))
			pending.push_back({edgeLen, index, index+1});
	}

	std::sort(begin(pending), end(pending),[&](Edge first, Edge sec){return first.len<sec.len;});
	for(auto [len, first, sec]: pending) if(dsu.root(first)!=dsu.root(sec)){
		dsu.join(first, sec);
		result+=len;
	}

	for(int i=0; i<(int)dsu.data.size(); ++i)
		assert(dsu.root(i)==dsu.root(0));

	return result;
}

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