Submission #506120

#	Time	Username	Problem	Language	Result	Execution time	Memory
506120		Jomnoi	Torrent (COI16_torrent)	C++17	69 / 100	360 ms	29072 KiB

torrent

#include <bits/stdc++.h>
#define DEBUG 0
using namespace std;

const int N = 3e5 + 10;
const int INF = 1e9 + 7;

vector <int> arr;
vector <int> adj[N];

bool find(int u, int p, int x) {
    if(u == x) {
        arr.push_back(u);
        return 1;
    }

    for(auto v : adj[u]) {
        if(v == p) { 
            continue;
        }

        if(find(v, u, x) == true) {
            arr.emplace_back(u);
            return true;
        }
    }
    return false;
}

int dfs(int u, int p, int x) {
    vector <int> child;
    for(auto v : adj[u]) {
        if(v == p || v == x) {
            continue;
        }

        child.push_back(dfs(v, u, x));
    }

    sort(child.rbegin(), child.rend());
    int res = 0;
    for(int i = 1; i <= child.size(); i++) {
        res = max(res, child[i - 1] + i);
    }
    return res;
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int n, a, b;
    cin >> n >> a >> b;
    for(int i = 1; i < n; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].emplace_back(v);
        adj[v].emplace_back(u);
    }

    find(a, -1, b);

    int l = 0, r = arr.size() - 2;
    int ans = INF;
    while(l <= r) {
        int mid = (l + r) / 2;

        int L = dfs(a, -1, arr[mid]);
        int R = dfs(b, -1, arr[mid + 1]);
        ans = min(ans, max(L, R));
        if(L < R) {
            l = mid + 1;
        }
        else {
            r = mid - 1;
        }
    }
    cout << ans;
    return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int dfs(int, int, int)':
torrent.cpp:42:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |     for(int i = 1; i <= child.size(); i++) {
      |                    ~~^~~~~~~~~~~~~~~

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