Submission #1213630

#	Time	Username	Problem	Language	Result	Execution time	Memory
1213630		iamhereforfun	Torrent (COI16_torrent)	C++20	100 / 100	231 ms	26004 KiB

torrent

// IamHereForFun //

#include <bits/stdc++.h>

using namespace std;

const int N = 3e5 + 5;
const int M = 1e2 + 5;
const int LG = 20;
const int S = 1e5 + 5;
const int P = 37;
const int INF = 1e9 + 5;
const int MOD = 1e9 + 7;

int n, st1, st2, dp[N], res;
vector<int> adj[N], path;

bool dfs1(int c, int p)
{
    if (c == st2)
    {
        path.push_back(c);
        return true;
    }
    for (int i : adj[c])
    {
        if (i == p)
            continue;
        if (dfs1(i, c))
        {
            path.push_back(c);
            return true;
        }
    }
    return false;
}

void dfs2(int c, int p, int id)
{
    dp[c] = 0;
    vector<int> v;
    for (int i : adj[c])
    {
        if (i == p)
            continue;
        if (i == path[id])
            continue;
        dfs2(i, c, id);
        v.push_back(dp[i]);
    }
    sort(v.rbegin(), v.rend());
    for (int x = 0; x < v.size(); x++)
    {
        v[x] += x + 1;
        dp[c] = max(dp[c], v[x]);
    }
}

void solve()
{
    cin >> n >> st1 >> st2;
    if (st1 > st2)
        swap(st1, st2);
    for (int x = 0; x < n - 1; x++)
    {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    dfs1(st1, 0);
    reverse(path.begin(), path.end());
    // for(int i : path) cout << i << " ";
    // cout << "\n";
    int l = 0, r = path.size() - 2, ans = 0;
    while (l <= r)
    {
        int m = (l + r) / 2;
        dfs2(st1, 0, m + 1);
        dfs2(st2, 0, m);
        // cout << "\n";
        if (dp[st1] <= dp[st2])
        {
            l = m + 1;
            ans = m;
        }
        else
        {
            r = m - 1;
        }
    }
    // cout << ans << "\n";
    dfs2(st1, 0, ans + 1);
    dfs2(st2, 0, ans);
    // cout << "\n";
    // for (int x = 1; x <= n; x++)
    // {
    //     cout << dp[x] << " " << x << "\n";
    // }
    res = max(dp[st1], dp[st2]);
    if (ans + 2 < path.size())
    {
        dfs2(st1, 0, ans + 2);
        dfs2(st2, 0, ans + 1);
        res = min(res, max(dp[st1], dp[st2]));
    }
    cout << res;
}

signed main()
{
    // freopen("CP.INP", "r", stdin);
    // freopen("CP.OUT", "w", stdout);
    // freopen("promote.in", "r", stdin);
    // freopen("promote.out", "w", stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    // cin >> t;
    for (int x = 1; x <= t; x++)
    {
        solve();
    }
    return 0;
}

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