Submission #841571

#	Time	Username	Problem	Language	Result	Execution time	Memory
841571		TheLostCookie	Longest Trip (IOI23_longesttrip)	C++17	100 / 100	10 ms	856 KiB

longesttrip

#include "longesttrip.h"
#include <functional>
#include <vector>

std::vector<int> longest_trip(int N, int D) {
	//Invariant: l0.back() and l1.back() are NOT connected.
	std::vector<int> l0,l1;
	
	auto mergeLines = [&l0, &l1]()->void{
		while(!l1.empty()) {
			l0.push_back(l1.back());
			l1.pop_back();
		}
		return;
	};
	
	auto q = [](int u, int v)->bool{
		return are_connected({u},{v});
	};
	
	l0.push_back(0);
	int u=1;
	while(u<N) {
		if(l1.empty()) {
			(q(l0.back(),u)?l0:l1).push_back(u);
			u++;
		} else if(u==N-1) {
			if(!q(l0.back(),u)) l1.push_back(u);
			else {
				l0.push_back(u);
				if(q(l1.back(),u)) {
					mergeLines();
				}
			}
			u++;
		} else {
			int v=u+1;
			bool b0 = q(l0.back(),u), b1 = q(l1.back(),v), b2 = q(u,v);
			if(b0&&b1) {
				l0.push_back(u);
				l1.push_back(v);
				if(b2) mergeLines();
			} else if(!b0&&!b1) {
				l0.push_back(v);
				l1.push_back(u);
				if(b2) mergeLines();
			} else if(b0&&!b1) {
				if(b2) {
					l0.push_back(u);
					l0.push_back(v);
				} else {
					l1.push_back(u);
					l0.push_back(v);
				}
			} else {
				if(b2) {
					l1.push_back(v);
					l1.push_back(u);
				} else {
					l0.push_back(v);
					l1.push_back(u);
				}
			}
			u+=2;
		}
	}
	
	if(l1.empty()) return l0;
	else if(!are_connected(l0,l1)) {
		if(l0.size()>l1.size()) return l0;
		else return l1;
	} else if(l0.size()>1&&(!are_connected({l0.front()},{l0.back()}))) {
		std::reverse(l0.begin(),l0.end());
		mergeLines();
		return l0;
	} else if(l1.size()>1&&(!are_connected({l1.front()},{l1.back()}))) {
		std::reverse(l1.begin(),l1.end());
		mergeLines();
		return l0;
	} else {
		std::vector<int> le(l0), ri(l1);
		for(int rep = 0; rep < 2; rep++) {
			while(le.size()>1) {
				std::vector<int> le0,le1;
				for(int i = 0; i < int(le.size()); i++) {
					(i%2?le0:le1).push_back(le[i]);
				}
				if(are_connected(le0,ri)) std::swap(le,le0);
				else std::swap(le,le1);
			}
			swap(le,ri);
		}
		int lei = 0, rii = 0;
		while(l0[lei] != le[0]) lei++;
		while(l1[rii] != ri[0]) rii++;
		
		std::vector<int> ans;
		for(int i = 0; i < int(l0.size()); i++) {
			ans.push_back(l0[(lei+i+1)%l0.size()]);
		}
		for(int i = 0; i < int(l1.size()); i++) {
			ans.push_back(l1[(rii+i)%l1.size()]);
		}
		return ans;
	}
}

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 60 / 60