oj.uz

답안 #1067805

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
1067805 2024-08-21T03:32:48 Z 12345678 Torrent (COI16_torrent) C++17
100 / 100
 237 ms 27156 KB 
#include <bits/stdc++.h>

using namespace std;

const int nx=3e5+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<(int)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;
    int l=0, r=cut.size()-1;
    while (l<r)
    {
        int md=(l+r)/2;
        //cout<<"here "<<cut[md]<<'\n';
        res=min(res, cost(cut[md]));
        if (dp[b]>dp[a]) r=md;
        else l=md+1;
    }
    cout<<min(res, cost(cut[l]));
}

Subtask #1
31.0 / 31.0

# 결과 실행 시간 메모리 Grader output
1 Correct 3 ms 7512 KB Output is correct
2 Correct 3 ms 7516 KB Output is correct
3 Correct 3 ms 7516 KB Output is correct

Subtask #2
69.0 / 69.0

# 결과 실행 시간 메모리 Grader output
1 Correct 210 ms 24148 KB Output is correct
2 Correct 223 ms 25536 KB Output is correct
3 Correct 220 ms 26824 KB Output is correct
4 Correct 237 ms 26292 KB Output is correct
5 Correct 222 ms 23632 KB Output is correct
6 Correct 216 ms 24140 KB Output is correct
7 Correct 219 ms 27156 KB Output is correct