Submission #632057

#	Time	Username	Problem	Language	Result	Execution time	Memory
632057		TimDee	Thousands Islands (IOI22_islands)	C++17	17.35 / 100	39 ms	9420 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;

int n,m;
vector<int> u,v;

vector<int> vis(1e5+3,0);
vector<int> par(1e5+3,-1);
vector<vector<int>> adj(1e5+3,vector<int>(0));

variant<bool, std::vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {

  n=N,m=M,u=U,v=V;
  if (n==2) {
    vector<int> fv,sv;
    for (int x=0; x<m; ++x) if (u[x]==0) fv.push_back(x); else sv.push_back(x);
      int f=fv.size(), s=sv.size();
    if (f>=2 && s) {
      vector<int> r={fv[0],sv[0],fv[1],fv[0],sv[0],fv[1]};;
      return r;
    } 
    else return false;
  }

  if (n<=400 && m==n*(n-1)) {

    int a,b,c,d; 
    for (int i=0; i<m; ++i) {
      if (u[i]==0 && v[i]==1) a=i;
      if (u[i]==0 && v[i]==2) b=i;
      if (u[i]==1 && v[i]==0) c=i;
      if (u[i]==2 && v[i]==0) d=i;
    }
    vector<int> r = {a,c,b,d,c,a,d,b};
    return r;

  }

  int _p3=1, _p4=1;
  for (int i=0; i<m; i+=2) {
    _p3&=((u[i]==v[i+1])&&(v[i]==u[i+1]));
    _p4&=((u[i]==u[i+1])&&(v[i]==v[i+1]));
  }

  if (_p3) {

    vector<int> deg(1e5+3,0);
    for (int i=0; i<m; i+=2) {
      deg[u[i]]++;
      deg[v[i]]++;
      adj[u[i]].push_back(v[i]);
      adj[v[i]].push_back(u[i]);
    }

    int mx=0;
    for (auto x:deg) mx=max(mx,x);
    if (mx<3) return false;

    if (deg[0]>=3) {
      int a=-1,b=-1,c=-1,d=-1;
      int f=-1,s=-1;
      for (auto x:adj[0]) {
        if (f==-1) f=x;
        else {s=x; break;}
      }
      for (int i=0; i<m; ++i) {
        if (u[i]==0 && v[i]==f) a=i;
        if (u[i]==0 && v[i]==s) b=i;
        if (u[i]==f && v[i]==0) c=i;
        if (u[i]==s && v[i]==0) d=i;
      }
      vector<int> r = {a,c,b,d,c,a,d,b};
      return r;
    }

    vis[0]=1;
    queue<int> q; q.push(0);
    while (!q.empty()) {
      int x=q.front(); q.pop();
      if (deg[x]>=3) {

        vector<int> r;
        int a,b,c,d;
        vector<int> path;
        int p=x;
        while (p!=0) {
          p=par[p];
          path.push_back(p);
        }
        for (int i=path.size()-1; i>=0; --i) r.push_back(path[i]);
        return r;

      }
      for (auto y:adj[x]) {
        if (!vis[y]) {
          q.push(y);
          vis[y]=1;
          par[y]=x;
        }
      }
    }

    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:84:13: warning: unused variable 'a' [-Wunused-variable]
   84 |         int a,b,c,d;
      |             ^
islands.cpp:84:15: warning: unused variable 'b' [-Wunused-variable]
   84 |         int a,b,c,d;
      |               ^
islands.cpp:84:17: warning: unused variable 'c' [-Wunused-variable]
   84 |         int a,b,c,d;
      |                 ^
islands.cpp:84:19: warning: unused variable 'd' [-Wunused-variable]
   84 |         int a,b,c,d;
      |                   ^
islands.cpp:108:1: warning: control reaches end of non-void function [-Wreturn-type]
  108 | }
      | ^
islands.cpp:35:37: warning: 'd' may be used uninitialized in this function [-Wmaybe-uninitialized]
   35 |     vector<int> r = {a,c,b,d,c,a,d,b};
      |                                     ^
islands.cpp:35:37: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:35:37: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:35:37: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45