Submission #1077755

#	Time	Username	Problem	Language	Result	Execution time	Memory
1077755		Faisal_Saqib	Thousands Islands (IOI22_islands)	C++17	10 / 100	124 ms	21616 KiB

islands

#include <bits/stdc++.h>
#include <variant>
#include <vector>
using namespace std;
const int N=1e3+100;
int n,m;
vector<int> adj[N];
int color[N],parent[N];
map<pair<int,int>,int> helper;
int cycle_start, cycle_end;

bool dfs(int v) {
    color[v] = 1;
    for (int u : adj[v]) {
        if(u==parent[v])continue;
        if (color[u] == 0) {
            parent[u] = v;
            if (dfs(u))
                return true;
        } else if (color[u] == 1) {
            if(u==0)
            {
                cycle_end = v;
                cycle_start = u;
            }
            return true;
        }
    }
    color[v] = 2;
    return false;
}

vector<int> find_cycle() {
    for(int i=0;i<n;i++)
    {
        color[i]=0;
        parent[i]=-1;
    }
    cycle_start = -1;

    for (int v = 0; v < n; v++) {
        if (color[v] == 0 && dfs(v))
            break;
    }

    if (cycle_start == -1) {
        return {};
    } else {
        vector<int> cycle;
        cycle.push_back(cycle_start);
        for (int v = cycle_end; v!=cycle_start; v = parent[v])
            cycle.push_back(v);
        cycle.push_back(cycle_start);
        reverse(cycle.begin(), cycle.end());
        return cycle;
    }
}
std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> v1, std::vector<int> v2)
{
    n=N,m=M;
    map<pair<int,int>,vector<int>> cnt;
    for(int j=0;j<m;j++)
        cnt[{v1[j],v2[j]}].push_back(j);
    if(n>400)
    {
        for(int j=0;j<m;j++)
        {
            helper[{v1[j],v2[j]}]=j;
            adj[v1[j]].push_back(v2[j]);
        }
        vector<int> cur=find_cycle();
        if(cur.size()==0)
        {
            return false;
        }
        else
        {
            vector<int> ed;
            vector<int> oth;
            for(int i=1;i<(cur.size());i++)
            {
                ed.push_back(helper[{cur[i-1],cur[i]}]);
                int fp=ed.back();
                oth.push_back(fp+((fp%2==0)?1:-1));
            }
            vector<int> ans;
            for(auto i:ed)
            {
                ans.push_back(i);
            }
            reverse(begin(oth),end(oth));
            for(auto i:oth)
            {
                ans.push_back(i);
            }
            reverse(begin(ans),end(ans));
            for(auto i:ans){
                ans.push_back(i);
            }
            reverse(begin(oth),end(oth));
            for(auto i:oth)
            {
                ans.push_back(i);
            }
            // found a cycle start at zero
        }
    }
    else if(n>2)
    {
        int edge01=cnt[{0,1}][0];
        int edge10=cnt[{1,0}][0];
        int edge02=cnt[{0,2}][0];
        int edge20=cnt[{2,0}][0];
        int edge12=cnt[{1,2}][0];
        int edge21=cnt[{2,1}][0];
        return vector<int>({edge01,edge12,edge20,edge02,edge21,edge10,edge20,edge12,edge01,edge10,edge21,edge02});
    }
    else if(cnt[{0,1}].size()>=2 and cnt[{1,0}].size()>=1)
    {
        int f=cnt[{0,1}][0];
        int s=cnt[{0,1}][1];
        int th=cnt[{1,0}][0];
        return vector<int>({f,th,s,f,th,s});
    }
    else
    {
        return false;
    }
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:80:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   80 |             for(int i=1;i<(cur.size());i++)
      |                         ~^~~~~~~~~~~~~
islands.cpp:61:36: warning: control reaches end of non-void function [-Wreturn-type]
   61 |     map<pair<int,int>,vector<int>> cnt;
      |                                    ^~~

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 0 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45