Submission #1067748

#	Time	Username	Problem	Language	Result	Execution time	Memory
1067748		12345678	Torrent (COI16_torrent)	C++17	0 / 100	24 ms	15444 KiB

torrent

#include <bits/stdc++.h>

using namespace std;

const int nx=1e5+5;

int n, a, b, u, v, dp[nx], res=INT_MAX;
vector<pair<int, int>> d[nx];
pair<int, int> pa[nx];
vector<int> cut;

void dfspa(int u, int p)
{
    for (auto [v, idx]:d[u]) if (v!=p) pa[v]={u, idx}, dfspa(v, u);
}

void dfs(int u, int p, int c)
{
    dp[u]=0;
    vector<int> s;
    for (auto [v, idx]:d[u]) if (v!=p&&idx!=c) dfs(v, u, c), s.push_back(dp[v]);
    sort(s.begin(), s.end());
    reverse(s.begin(), s.end());
    for (int i=0; i<s.size(); i++) dp[u]=max(dp[u], i+1+s[i]);
}

int cost(int x)
{
    dfs(a, a, x);
    dfs(b, b, x);
    return max(dp[a], dp[b]);
}

int main()
{
    cin.tie(NULL)->sync_with_stdio(false);
    cin>>n>>a>>b;
    for (int i=1; i<n; i++) cin>>u>>v, d[u].push_back({v, i}), d[v].push_back({u, i});
    dfspa(a, a);
    int tmp=b;
    while (tmp!=a) cut.push_back(pa[tmp].second), tmp=pa[tmp].first;
    //for (int i=0; i<cut.size(); i++) cout<<"cost "<<cost(cut[i])<<'\n';
    int l=0, r=cut.size()-1;
    while (l<r)
    {
        int md=(l+r+1)/2;
        //cout<<"debug "<<l<<' '<<r<<' '<<md<<'\n';
        if (cost(cut[md])<cost(cut[md-1])) l=md;
        else r=md-1;
    }
    cout<<cost(cut[l]);
}

Compilation message (stderr)

torrent.cpp: In function 'void dfs(int, int, int)':
torrent.cpp:24:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for (int i=0; i<s.size(); i++) dp[u]=max(dp[u], i+1+s[i]);
      |                   ~^~~~~~~~~

• Subtask 1: 0 / 31
• Subtask 2: 0 / 69