Submission #743550

#	Time	Username	Problem	Language	Result	Execution time	Memory
743550		lukadupli	Torrent (COI16_torrent)	C++14	100 / 100	613 ms	25800 KiB

torrent

#include <bits/stdc++.h>

using namespace std;

const int MAXN = 3e5 + 5;

int n, a, b, xe, ye;
vector<int> adj[MAXN];

int dfs(int node, int parent = -1){
    int res = 0;

    vector<int> v;
    for(int nxt : adj[node]){
        if(nxt != parent &&
           (min(xe, ye) != min(node, nxt) || max(xe, ye) != max(node, nxt))) v.push_back(dfs(nxt, node));
    }

    sort(v.begin(), v.end(), greater<int>());

    for(int i = 0; i < v.size(); i++) res = max(res, v[i] + i + 1);

    return res;
}

vector<int> path;
bool found = 0;
void dfs2(int node, int parent = -1){
    path.push_back(node);
    if(node == b){
        found = 1;
        return;
    }

    for(int nxt : adj[node]){
        if(nxt != parent) dfs2(nxt, node);
        if(found) return;
    }

    path.pop_back();
}


int main()
{
    cin >> n >> a >> b;
    for(int i = 0; i < n - 1; i++){
        int x, y;
        cin >> x >> y;

        adj[x].push_back(y);
        adj[y].push_back(x);
    }

    dfs2(a, -1);

    int l = 0, r = path.size() - 2;
    while(r > l){
        int m = (l + r) / 2;

        xe = path[m]; ye = path[m + 1];
        int A = dfs(a), B = dfs(b);

        if(A < B) l = m + 1;
        else r = m;
    }

    xe = path[l]; ye = path[l + 1];
    int s1 = max(dfs(a), dfs(b));

    int s2 = 1e9;
    if(l > 0){
        xe = path[l - 1]; ye = path[l];
        s2 = max(dfs(a), dfs(b));
    }

    cout << min(s1, s2);

	return 0;
}

Compilation message (stderr)

torrent.cpp: In function 'int dfs(int, int)':
torrent.cpp:21:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |     for(int i = 0; i < v.size(); i++) res = max(res, v[i] + i + 1);
      |                    ~~^~~~~~~~~~

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