Submission #1028577

#	Time	Username	Problem	Language	Result	Execution time	Memory
1028577		Thanhs	Mousetrap (CEOI17_mousetrap)	C++14	100 / 100	542 ms	194004 KiB

mousetrap

#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
// #define int long long
// #define double long double
 
#define endl '\n'
#define fastIO ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
#define setmin(x, y) x = min((x), (y))
#define setmax(x, y) x = max((x), (y))
#define sqr(x) ((x) * (x))
#define fi first
#define se second
 
// mt19937 hdp(chrono::high_resolution_clock::now().time_since_epoch().count());
// int rand(int l, int r){return l + ((hdp() % (r - l + 1)) + r - l + 1) % (r - l + 1);}
 
const int NM = 1e6 + 5;
const int mod = 1e6 + 3;
const int inf = 1e9 + 1;

vector<int> g[NM];
int n, t, m, w[NM], W[NM], dep[NM], par[NM];
vector<pair<int, int>> L;

void dfs(int u = t, int p = 0)
{
    if (u != t)
        W[u] = W[par[u]] + max(0, (int)g[u].size() - 2);
    int be = 0, sb = 0;
    for (auto v : g[u])
    {
        if (v == p)
            continue;
        dep[v] = dep[u] + 1;
        par[v] = u;
        dfs(v, u);
        if (be < w[v])
        {
            sb = be;
            be = w[v];
        }
        else if (sb < w[v])
            sb = w[v];
    }
    if (g[u].size() - !!p == 0)
        w[u] = 0;
    else if (g[u].size() - !!p == 1)
        w[u] = 1;
    else 
        w[u] += sb + g[u].size() - !!p;
}

bool check(int x)
{
    int B = 0;
    for (auto p : L)
        if (p.se + B > x)
        {
            if (B > p.fi)
                return false;
            B++;
        }
    if (B > x)
        return false;
    return true;
}

signed main()
{
    if (fopen("in.txt", "r")) {
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
    }
    fastIO
    cin >> n >> t >> m;
    for (int i = 2; i <= n; i++)
    {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    dfs();
    int u = m, prv = 0;
    while (u != t)
    {
        for (auto v : g[u])
            if (v != prv && v != par[u])
                L.emplace_back(dep[m] - dep[u], w[v] + W[par[v]] + 1 - !!prv);
        prv = u;
        u = par[u];
    }
    // for (auto t : L)
    //     cout << t.fi << ' ' << t.se << endl;
    sort(L.begin(), L.end());
    int l = -1, r = 2 * n;
    while (l < r - 1)
    {
        int mid = l + r >> 1;
        if (check(mid))
            r = mid;
        else
            l = mid;
    }
    cout << r;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:101:21: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
  101 |         int mid = l + r >> 1;
      |                   ~~^~~
mousetrap.cpp:73:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |         freopen("in.txt", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:74:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |         freopen("out.txt", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 20 / 20
• Subtask 2: 25 / 25
• Subtask 3: 20 / 20
• Subtask 4: 35 / 35