Submission #1297803

#	Time	Username	Problem	Language	Result	Execution time	Memory
1297803		jahongir	Torrent (COI16_torrent)	C++20	69 / 100	660 ms	24880 KiB

torrent

// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
template<typename T> using ordered_set = tree<T,null_type,less_equal<T>,rb_tree_tag,
					 tree_order_statistics_node_update>;
 
#define ll long long
#define pi pair<int,int>
#define vi vector<int>
#define pb push_back
#define all(a) a.begin(),a.end()




const int mxn = 3e5+1;
vector<int> g[mxn];
int par[mxn],ver[mxn];
int dp[mxn], memo[mxn];
int v1,v2;

void pre_dfs(int u, int p){
    par[u] = p;
    for(auto v : g[u]) if(v!=p)
        pre_dfs(v,u);
}


void dfs(int u, int p){
    dp[u] = 0;

    vector<int> vec;
    for(auto v : g[u]) if(v!=p && v!=v1){
        dfs(v,u); vec.push_back(dp[v]);
    }

    int cnt = vec.size();
    sort(all(vec));

    for(int i = 0; i < cnt; i++)
        dp[u] = max(dp[u],vec[i]+cnt-i);
}


void solve(){
    int n,a,b; cin >> n >> a >> b;
    if(n==2){
        cout << 0; return;
    }

    for(int i = 1; i < n; i++){
        int u,v; cin >> u >> v;
        g[u].pb(v); g[v].pb(u);
    }

    pre_dfs(a,a);
    int l = 0, r = 0; ver[0] = b;
    int u = b;
    while(par[u]!=a){
        u = par[u]; ver[++r] = u;
    }
    ver[r+1] = a;

    while(l+3 < r){
        int m1 = l + (r-l)/3;
        int m2 = r - (r-l)/3;
        int r1 = memo[m1];
        if(r1==0){
            v1 = ver[m1]; dfs(a,a);
            v1 = ver[m1+1];dfs(b,b);
            r1 = memo[m1] = max(dp[a],dp[b]);
        }
        int r2 = memo[m2];
        if(r2==0){
            v1 = ver[m2]; dfs(a,a);
            v1 = ver[m2+1];dfs(b,b);
            r2 = memo[m2] = max(dp[a],dp[b]);
        }

        if(r1 <= r2) r = m2;
        else l = m1;
    }

    int ans = n;
    for(int i = l; i <= r; i++){
        int r1 = memo[i];
        if(r1==0){
            v1 = ver[i]; dfs(a,a);
            v1 = ver[i+1];dfs(b,b);
            r1 = memo[i] = max(dp[a],dp[b]);
        }
        ans = min(ans,r1);
    }

    cout << ans;

}


signed main(){
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
    // cin >> t;
    while(t--){solve();}
}

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