Submission #259841

#	Time	Username	Problem	Language	Result	Execution time	Memory
259841		Kastanda	Mousetrap (CEOI17_mousetrap)	C++11	100 / 100	1312 ms	229240 KiB

mousetrap

// M
#include<bits/stdc++.h>
using namespace std;
const int N = 1000006;
int n, root, st, SM, P[N], M[N], dp[N];
vector < int > Adj[N], V[N];
void DFS(int v, int p = 0)
{
    P[v] = p;
    for (int i = 0; i < (int)Adj[v].size(); i ++)
        if (Adj[v][i] == p)
            Adj[v].erase(Adj[v].begin() + i);
    if (st == v) M[v] = 1;
    for (int u : Adj[v])
        DFS(u, v), M[v] |= M[u];
    if (v == root)
    {
        int w = -1;
        for (int u : Adj[v])
            if (M[u]) w = u;
        Adj[v] = {w};
    }
}
void DFS2(int v, int p = 0)
{
    if (v != root)
        SM += (int)Adj[v].size() - (M[v] && v != st);
    for (int u : Adj[v])
        DFS2(u, v);
    if (v != root)
        SM -= (int)Adj[v].size() - (M[v] && v != st);
    for (int u : Adj[v])
        if (!M[u])
            V[v].push_back(dp[u]);
    sort(V[v].begin(), V[v].end());
    reverse(V[v].begin(), V[v].end());
    if (M[v])
        return ;
    if (!Adj[v].size())
    {
        dp[v] = SM;
        return ;
    }
    if (Adj[v].size() == 1)
    {
        dp[v] = SM + 1;
        return ;
    }
    dp[v] = V[v][1];
}
inline bool Solve(int md)
{
    int nw = st, cnt = 1;
    while (nw != root)
    {
        int c = 0;
        for (int val : V[nw])
            if (val > md)
                cnt --, c ++;
        md -= c;
        if (cnt < 0 || md < 0)
            return 0;
        nw = P[nw];
        cnt ++;
    }
    return 1;
}
int main()
{
    scanf("%d%d%d", &n, &root, &st);
    for (int i = 1; i < n; i ++)
    {
        int v, u;
        scanf("%d%d", &v, &u);
        Adj[v].push_back(u);
        Adj[u].push_back(v);
    }
    DFS(root);
    DFS2(root);
    int le = -1, ri = n, md;
    while (ri - le > 1)
    {
        md = (le + ri) >> 1;
        if (Solve(md))
            ri = md;
        else
            le = md;
    }
    return !printf("%d\n", ri);
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:70:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d%d", &n, &root, &st);
     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:74:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &v, &u);
         ~~~~~^~~~~~~~~~~~~~~~

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