Submission #1099202

#	Time	Username	Problem	Language	Result	Execution time	Memory
1099202		MMihalev	Highway Tolls (IOI18_highway)	C++14	100 / 100	180 ms	20104 KiB

highway

#include "highway.h"
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
using namespace std;
const int MAX_N=90005;
int q;
int remedges;
int n,m;
vector<int>w;
vector<pair<int,int> >g[MAX_N],G[MAX_N];
long long edges,cost;
int root;
int a,b;
int parent[MAX_N];
int paredge[MAX_N];
int depth[MAX_N];
vector<int>ENDS;
vector<pair<int,int>>nodes;
bool used[MAX_N];
bool usededge[130010];
void initbfs()
{
    queue<int>q;
    q.push(root);
    used[root]=1;

    while(q.size())
    {
        int u=q.front();
        q.pop();

        for(auto [v,edge]:G[u])
        {
            if(used[v])continue;

            used[v]=1;
            usededge[edge]=1;
            g[u].push_back({v,edge});
            g[v].push_back({u,edge});
            parent[v]=u;
            paredge[v]=edge;
            depth[v]=depth[u]+1;
            q.push(v);
        }
    }
}
int onpath()
{
    vector<pair<int,int>>node;
    for(int i=0;i<n;i++)
    {
        node.push_back({G[i].size(),i});
    }
    sort(node.begin(),node.end());

    int l=0,r=n-1;
    int ans;

    while(l<=r)
    {
        int mid=(l+r)/2;
        for(int u=0;u<=mid;u++)
        {
            for(auto [v,edge]:G[node[u].second])
            {
                w[edge]=1;
            }
        }
        long long ncost=ask(w);q++;
        for(int u=0;u<=mid;u++)
        {
            for(auto [v,edge]:G[node[u].second])
            {
                w[edge]=0;
            }
        }
        if(ncost!=cost)
        {
            ans=node[mid].second;
            r=mid-1;
        }
        else l=mid+1;
    }

    return ans;
}
void nodesdfs(int u)
{
    if(remedges==edges)
    {
        if(depth[u]<=remedges)nodes.push_back({depth[u],u});
    }
    else if(depth[u]==remedges)nodes.push_back({depth[u],u});

    for(auto [v,edge]:g[u])
    {
        if(v==parent[u])continue;

        nodesdfs(v);
    }
}
int rec(int l,int r)
{
    if(l==r)
    {
        return nodes[l].second;
    }

    int mid=(l+r)/2;

    for(int i=l;i<=mid;i++)
    {
        w[paredge[nodes[i].second]]=1;
    }
    long long ncost=ask(w);q++;
    for(int i=l;i<=mid;i++)
    {
        w[paredge[nodes[i].second]]=0;
    }

    if(ncost!=cost)return rec(l,mid);
    return rec(mid+1,r);
}
void solve(int branch,bool with)
{
    nodes.clear();
    for(int i=0;i<g[root].size();i++)
    {
        if(with)
        {
            if(i!=branch)continue;
        }
        else
        {
            if(i==branch)continue;
        }

        nodesdfs(g[root][i].first);
    }
    sort(nodes.rbegin(),nodes.rend());
    ENDS.push_back(rec(0,nodes.size()-1));
}
int solvetwo()
{
    int l=0,r=g[root].size()-1;
    int ans=-1;

    while(l<=r)
    {
        int mid=(l+r)/2;

        for(int i=0;i<=mid;i++)
        {
            w[g[root][i].second]=1;
        }
        long long ncost=ask(w);q++;
        for(int i=0;i<=mid;i++)
        {
            w[g[root][i].second]=0;
        }

        if(ncost!=cost)
        {
            ans=mid;
            r=mid-1;
        }
        else l=mid+1;
    }

    return ans;
}
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B)
{
    n=N;
    m=U.size();
    w.resize(m);
    a=A;
    b=B;

    for(int i=0;i<m;i++)
    {
        G[U[i]].push_back({V[i],i});
        G[V[i]].push_back({U[i],i});
    }

    cost=ask(w);q++;
    edges=cost/a;
    remedges=edges;

    root=onpath();
    initbfs();
    for(int i=0;i<m;i++)
    {
        if(usededge[i])continue;
        w[i]=1;
    }

    int branch=solvetwo();
    solve(branch,1);
    if(depth[ENDS[0]]==edges)
    {
        ENDS.push_back(root);
    }
    else
    {
        remedges-=depth[ENDS[0]];
        solve(branch,0);
    }

    answer(ENDS[0],ENDS[1]);
}

Compilation message (stderr)

highway.cpp: In function 'void initbfs()':
highway.cpp:34:18: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   34 |         for(auto [v,edge]:G[u])
      |                  ^
highway.cpp: In function 'int onpath()':
highway.cpp:66:22: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   66 |             for(auto [v,edge]:G[node[u].second])
      |                      ^
highway.cpp:74:22: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   74 |             for(auto [v,edge]:G[node[u].second])
      |                      ^
highway.cpp: In function 'void nodesdfs(int)':
highway.cpp:97:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   97 |     for(auto [v,edge]:g[u])
      |              ^
highway.cpp: In function 'void solve(int, bool)':
highway.cpp:129:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  129 |     for(int i=0;i<g[root].size();i++)
      |                 ~^~~~~~~~~~~~~~~
highway.cpp: In function 'int onpath()':
highway.cpp:87:12: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
   87 |     return ans;
      |            ^~~

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 6 / 6
• Subtask 4: 33 / 33
• Subtask 5: 18 / 18
• Subtask 6: 31 / 31