Submission #1163200

#	Time	Username	Problem	Language	Result	Execution time	Memory
1163200		kiethm07	Torrent (COI16_torrent)	C++20	100 / 100	264 ms	45504 KiB

torrent

#include <bits/stdc++.h>

#define pii pair<int,int>
#define fi first
#define se second

#define all(x) (x).begin(),(x).end()
#define compact(x) (x).erase(all(x),(x).end())
#define pb(x) push_back(x)

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

using namespace std;

const int inf = 1e9;
const ll linf = 1e18;
const double pi = acos(-1);
const int N = 3e5 + 5;
const int LOG = 32 - __builtin_clz(N);

vector<int> a[N];
int n;
int r1, r2;
int pa[N][LOG];
int h[N];

void dfs(int u,int p = -1){
    for (int i = 1; (1 << i) <= h[u]; i++){
        pa[u][i] = pa[pa[u][i-1]][i-1];
    }
    for (int i = 0; i < a[u].size(); i++){
        int v = a[u][i];
        if (v == p) continue;
        pa[v][0] = u;
        h[v] = h[u] + 1;
        dfs(v,u);
    }
}

int cal(int u,int p,int f){
    vector<int> tmp;
    for (int v : a[u]){
        if (v == p || v == f) continue;
        tmp.push_back(cal(v,u,f));
    }
    int res = 0;
    sort(all(tmp),greater<int>());
    int k = 0;
    for (int i = 0; i < tmp.size(); i++){
        k = max(tmp[i] + i + 1,k);
    }
    res += k;
    return res;
}

int getAns(int x){
    return max(cal(r1,-1,x), cal(r2,-1,pa[x][0]));
}

int solve(){
    if (pa[r2][0] == r1) return max(cal(r1,-1,r2),cal(r2,-1,r1));
    int res = r2;
    int k = 31 - __builtin_clz(h[r2] - 1);
    int step = 0;
    for (int i = k; i >= 0; i--){
        if (step + (1 << i) > h[r2] - 1) continue;
        int tmp = pa[res][i];
//        cout << tmp << " " << check(tmp) << "\n";
        int f = cal(r1,-1,tmp);
        int g = cal(r2,-1,pa[tmp][0]);
        if (f >= g){
            res = tmp;
            step += (1 << i);
        }
    }
//    cout << res << "\n";
//    return getAns(res);
    return min(getAns(res),getAns(pa[res][0]));
}

int solve2(){
    int cur = r2;
    int res = inf;
    while(cur != r1){
        int tmp = getAns(cur);
        cout << tmp << "\n";
        res = min(res,tmp);
        cur = pa[cur][0];
    }
    return res;
}

int main(){
    cin.tie(0) -> sync_with_stdio(0);
    #define TEXT "torrent"
    if (fopen(TEXT".inp","r")){
        freopen(TEXT".inp","r",stdin);
        freopen(TEXT".out","w",stdout);
    }
    cin >> n >> r1 >> r2;
    for (int i = 1; i < n; i++){
        int u,v;
        cin >> u >> v;
        a[u].push_back(v);
        a[v].push_back(u);
    }
    dfs(r1);
    cout << solve() << "\n";
//    cout << solve2() << "\n";
    return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int main()':
torrent.cpp:99:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   99 |         freopen(TEXT".inp","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:100:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  100 |         freopen(TEXT".out","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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