Submission #1212679

#	Time	Username	Problem	Language	Result	Execution time	Memory
1212679		Aviansh	Longest Trip (IOI23_longesttrip)	C++20	85 / 100	6 ms	424 KiB

longesttrip

#include "longesttrip.h"

#include <bits/stdc++.h>

using namespace std;

vector<int> longest_trip(int n, int D) {
    if(D==3){
        vector<int>ans(n);
        iota(ans.begin(),ans.end(),0);
        return ans;
    }

    if(D==2){
        set<int>lef;
        for(int i = 0;i<n;i++){
            lef.insert(i);
        }
        vector<int>ans;
        ans.push_back(0);
        lef.erase(0);
        while(lef.size()>1){
            if(are_connected({ans.back()},{*lef.begin()})){
                ans.push_back(*lef.begin());
                lef.erase(lef.begin());
            }
            else{
                ans.push_back(*(++lef.begin()));
                lef.erase(++lef.begin());
            }
        }
        if(are_connected({*lef.begin()},{ans.back()})){
            ans.push_back(*lef.begin());
            return ans;
        }
        ans.insert(ans.begin(),*lef.begin());
        return ans;
    }

    assert(D==1);
    vector<int>pt1,pt2;
    vector<int>order(n);
    iota(order.begin(),order.end(),0);
    random_shuffle(order.begin(),order.end());
    pt1.push_back(order[0]);
    for(int i = 1;i<n;i++){
        int prev1 = pt1.back();
        if(are_connected({prev1},{order[i]})){
            pt1.push_back(order[i]);
            continue;
        }
        //not adjacent.
        if(pt2.size()){
            int prev2 = pt2.back();
            if(are_connected({prev2},{order[i]})){
                pt2.push_back(order[i]);
            }
            else{
                reverse(pt2.begin(),pt2.end());
                pt1.insert(pt1.end(),pt2.begin(),pt2.end());
                pt2.clear();
                i--;
                continue;
            }
        }
        else{
            pt2.push_back(order[i]);
        }
    }
    if(pt2.size()==0){
        return pt1;
    }
    if(!are_connected(pt1,pt2)){
        if(pt1.size()>pt2.size()){
            return pt1;
        }
        return pt2;
    }
    vector<int>t1;
    if(pt1.size()==1){
        t1.push_back(pt1[0]);
    }
    else{
        t1.push_back(pt1[0]);
        t1.push_back(pt1[pt1.size()-1]);
    }
    vector<int>t2;
    if(pt2.size()==1){
        t2.push_back(pt2[0]);
    }
    else{
        t2.push_back(pt2[0]);
        t2.push_back(pt2[pt2.size()-1]);
    }
    if(are_connected(t1,t2)){
        //ends connected
        if(are_connected({pt1[0]},{pt2[0]})){
            vector<int>ans;
            reverse(pt1.begin(),pt1.end());
            for(int i : pt1){
                ans.push_back(i);
            }
            for(int i : pt2){
                ans.push_back(i);
            }
            return ans;
        }
        //fronts
        if(are_connected({pt1[0]},{pt2[pt2.size()-1]})){
            vector<int>ans;
            for(int i : pt2){
                ans.push_back(i);
            }
            for(int i : pt1){
                ans.push_back(i);
            }
            return ans;
        }
        if(are_connected({pt1[pt1.size()-1]},{pt2[pt2.size()-1]})){
            vector<int>ans;
            for(int i : pt1){
                ans.push_back(i);
            }
            reverse(pt2.begin(),pt2.end());
            for(int i : pt2){
                ans.push_back(i);
            }
            return ans;
        }
        if(are_connected({pt1[pt1.size()-1]},{pt2[0]})){
            vector<int>ans;
            for(int i : pt1){
                ans.push_back(i);
            }
            for(int i : pt2){
                ans.push_back(i);
            }
            return ans;
        }
    }
    //both cycles now.
    //must find joiner.
    int lo1 = 0;
    int hi1 = pt1.size()-1;
    while(lo1<hi1){
        int mid = (lo1+hi1)/2;
        vector<int>quer;
        for(int i = 0;i<=mid;i++){
            quer.push_back(pt1[i]);
        }
        if(are_connected(quer,pt2)){
            hi1=mid;
        }
        else{
            lo1=mid+1;
        }
    }
    int lo2 = 0;
    int hi2 = pt2.size()-1;
    while(lo2<hi2){
        int mid = (lo2+hi2)/2;
        vector<int>quer;
        for(int i = 0;i<=mid;i++){
            quer.push_back(pt2[i]);
        }
        if(are_connected(quer,{pt1[lo1]})){
            hi2=mid;
        }
        else{
            lo2=mid+1;
        }
    }
    vector<int>ans;
    for(int i = 1;i<=pt1.size();i++){
        ans.push_back(pt1[(i+lo1)%(pt1.size())]);
    }
    for(int i = pt2.size();i>0;i--){
        ans.push_back(pt2[(i+lo2)%(pt2.size())]);
    }
    return ans;
}

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 45 / 60