#include <bits/stdc++.h>
using namespace std;
vector<int> longest_trip(int n, int d){
assert(d>0);
vector<vector<int> > chains;
for(int i=0; i<n; i++) chains.push_back({i});
mt19937 rng(999);
shuffle(chains.begin(),chains.end(),rng);
while((int)chains.size()>2){
vector<int> take[3];
for(int i=0; i<3; i++){
swap(take[i],chains[(int)chains.size()-i-1]);
}
chains.pop_back();
if(are_connected({take[0][0]},{take[2][0]})) swap(take[1],take[2]);
else if(are_connected({take[1][0]},{take[2][0]})) swap(take[0],take[2]);
reverse(take[0].begin(),take[0].end());
for(int i:take[1]) take[0].push_back(i);
take[1].clear();
swap(chains[(int)chains.size()-1],take[0]);
swap(chains[(int)chains.size()-2],take[2]);
}
assert((int)chains.size()==2);
if(are_connected(chains[0],chains[1])){
int lo=0,hi=chains[1].size()-1,mid;
vector<int> hehe;
while(lo<hi){
hehe.clear();
mid=(lo+hi)/2;
for(int i=lo; i<=mid; i++) hehe.push_back(chains[1][i]);
if(are_connected(chains[0],hehe)) hi=mid;
else lo=mid+1;
}
int m2=chains[1][lo];
lo=0,hi=chains[0].size()-1;
while(lo<hi){
hehe.clear();
mid=(lo+hi)/2;
for(int i=lo; i<=mid; i++) hehe.push_back(chains[0][i]);
if(are_connected({m2},hehe)) hi=mid;
else lo=mid+1;
}
int m1=chains[0][lo];
if(m2!=chains[1][0]&&m2!=chains[1].back()){
if(are_connected({m1},{chains[1].back()})){
reverse(chains[1].begin(),chains[1].end());
}
else if(are_connected({chains[1][0]},{chains[1].back()})){
hehe.clear();
while(!chains[1].empty()){
if(chains[1].back()==m2) break;
hehe.push_back(chains[1].back());
chains[1].pop_back();
}
reverse(chains[1].begin(),chains[1].end());
for(int i:hehe) chains[1].push_back(i);
}
}
else if(m2==chains[1].back()) reverse(chains[1].begin(),chains[1].end());
if(m1==chains[0].back()){
for(int i:chains[1]) chains[0].push_back(i);
return chains[0];
}
else if(m1==chains[0][0]){
reverse(chains[0].begin(),chains[0].end());
for(int i:chains[1]) chains[0].push_back(i);
return chains[0];
}
else{
if(are_connected({chains[0][0]},{chains[1].back()})){
for(int i:chains[0]) chains[1].push_back(i);
return chains[1];
}
else if(are_connected({chains[0].back()},{chains[1].back()})){
reverse(chains[1].begin(),chains[1].end());
for(int i:chains[1]) chains[0].push_back(i);
return chains[0];
}
else{
hehe.clear();
while(!chains[0].empty()){
if(chains[0].back()==m2) break;
hehe.push_back(chains[0].back());
chains[0].pop_back();
}
vector<int> ans;
while(!hehe.empty()){
ans.push_back(hehe.back());
hehe.pop_back();
}
for(int i:chains[0]) ans.push_back(i);
for(int i:chains[1]) ans.push_back(i);
return ans;
}
}
}
else{
if(chains[0].size()>chains[1].size()) return chains[0];
else return chains[1];
}
}
Compilation message
longesttrip.cpp: In function 'std::vector<int> longest_trip(int, int)':
longesttrip.cpp:15:6: error: 'are_connected' was not declared in this scope
15 | if(are_connected({take[0][0]},{take[2][0]})) swap(take[1],take[2]);
| ^~~~~~~~~~~~~
longesttrip.cpp:24:5: error: 'are_connected' was not declared in this scope
24 | if(are_connected(chains[0],chains[1])){
| ^~~~~~~~~~~~~
longesttrip.cpp:5:23: warning: control reaches end of non-void function [-Wreturn-type]
5 | vector<vector<int> > chains;
| ^~~~~~
