Submission #1118129

#	Time	Username	Problem	Language	Result	Execution time	Memory
1118129		vjudge1	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	683 ms	76472 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

#define TASK ""
#define REP(i, n) for(int i = 1; i <= n; i++)
#define FOR(i, a, b) for(auto i = a; i <= b; i++)
#define FORD(i, a, b) for(auto i = a; i >= b; i--)
template<class T> bool maximize(T& a, T b) { if(a < b) return a = b, 1; return 0; }
template<class T> bool minimize(T& a, T b) { if(a > b) return a = b, 1; return 0; }

#define sz(a) (int)(a.size())
using ii = pair<int, int>;
#define fi first
#define se second

mt19937 rng(time(0));

const int N = (int)1e6 + 7;
vector<int> adj[N];
vector<ii> save;
bool inPath[N];
int n, t, m;
int dp[N], dep[N];

void Read()
{
    cin >> n >> t >> m;
    REP(i, n - 1)
    {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
}

void DFS(int u, int p = 0)
{
    vector<int> cost;
    for(int v : adj[u])
    {
        if(v == p)
            continue;
        if(p)
            dp[v] = dp[u] + sz(adj[u]) - 2;
        DFS(v, u);
        cost.push_back(dp[v]);
        if(inPath[v])
            inPath[u] = 1;
    }
    sort(cost.begin(), cost.end(), greater<int>());
    if(sz(cost) > 1)
        dp[u] = cost[1];
    if(sz(adj[u]) > 1)
        dp[u]++;
}

void Run(int u, int p = -1)
{
    for(int v : adj[u])
    {
        if(v == p)
            continue;
        dep[v] = dep[u] + 1;
        if(inPath[u] && !inPath[v])
            save.push_back({dep[v], dp[v] + (u == m)});
        else
            Run(v, u);
    }
}

bool Check(int x)
{
    int need = 0;
    for(auto s : save)
    {
        if(need > s.fi && need + s.se > x)
            return 0;
        if(need + s.se > x)
            need++;
    }
    return need <= x;
}

void Solve()
{
    inPath[m] = 1;
    dep[m] = -1;
    DFS(t);
    Run(m);
    int l = 0, r = 1e9 + 7;
    sort(save.begin(), save.end());
    while(l + 1 < r)
    {
        int m = l + r >> 1;
        if(Check(m))
            r = m;
        else
            l = m;
    }
    cout << r << endl;
}

signed main(void)
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    if(fopen("TASK.INP", "r")) freopen("TASK.INP", "r", stdin);
    if(fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        freopen(TASK".OUT", "w", stdout);
    }

    Read();
    Solve();

    return 0;
}
/*
10 1 4
1 2
2 3
2 4
3 9
3 5
4 7
4 6
6 8
7 10
*/

Compilation message (stderr)

mousetrap.cpp: In function 'void Solve()':
mousetrap.cpp:96:19: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   96 |         int m = l + r >> 1;
      |                 ~~^~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:110:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  110 |     if(fopen("TASK.INP", "r")) freopen("TASK.INP", "r", stdin);
      |                                ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:113:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  113 |         freopen(TASK".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:114:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |         freopen(TASK".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 20
• Subtask 2: 25 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35