Submission #716187

#	Time	Username	Problem	Language	Result	Execution time	Memory
716187		socpite	Mousetrap (CEOI17_mousetrap)	C++14	0 / 100	978 ms	72428 KiB

mousetrap

#include<bits/stdc++.h>
using namespace std;

#define f first 
#define s second

typedef long double ld;
typedef pair<int, pair<int, int>> ftype;

const int maxn = 1e6+5;
const int inf = 1e9+5;

int n, m, t;
int l, r, mid;

vector<int> g[maxn];

int dp[maxn], onp[maxn];

void onp_dfs(int x, int p){
    if(x == t){
        onp[x] = 1;
        return;
    }
    for(auto v: g[x]){
        if(v == p)continue;
        onp_dfs(v, x);
        if(onp[v]){
            dp[x]--;
            onp[x] = 1;
        }
    }
    //cout << x << " " << dp[x] << endl;
}

void dfs(int x, int p){
    if(x == t)return;
    dp[x] += g[x].size()-(p!=0);
    for(auto v: g[x]){
        if(v == p)continue;
        dp[v] += dp[x];
        dfs(v, x);
    }
}

int dfs2(int x, int p, int tot = 0){
    if(x == t)return 0;
    for(auto v: g[x]){
        if(v == p)continue;
        if(onp[v])tot+=dfs2(v, x, 0);
    }
    dp[x] += tot;
    for(auto v: g[x]){
        if(v == p)continue;
        if(!onp[v])dfs2(v, x, tot);
    }
    if(onp[x])tot+=g[x].size()-(p!=0)-1;
    //  cout << x << " " << dp[x] << " " << tot << endl;
    return tot;
}

int chk(int x, int p){
    if(dp[x] > mid)return inf;
    if(x == t)return 0;
    int re = inf, base = -inf;
    vector<int> val;
    for(auto v: g[x]){
        if(v == p)continue;
        int tmp = chk(v, x);
        //cout << v << " " << tmp << endl;
        if(onp[v])base = tmp;
        else val.push_back(tmp);
    }
    sort(val.begin(), val.end());
    re = min(re, int(val.size()));
    if(!val.empty())re = min(re, max(val.back(), base));
    for(int i = 0; i < val.size(); i++){
        if(val[i] >= re)re = min(re, val[i] + int(val.size())-i-1);
    }
    re--;
    re = max(re, 0);
    return re;
}



int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    //freopen("mousetrap.inp", "r", stdin);
    // freopen("mousetrap.out", "w", stdout);
    cin >> n >> t >> m;
    for(int i = 0; i < n-1; i++){
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    onp_dfs(m, 0);
    dfs(m, 0);
    dfs2(m, 0);
    int l = 0, r = 2*n;
    while(l < r){
        mid = (l+r)>>1;
        if(!chk(m, 0))r = mid;
        else l = mid+1;
    }
    cout << l;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int chk(int, int)':
mousetrap.cpp:77:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   77 |     for(int i = 0; i < val.size(); i++){
      |                    ~~^~~~~~~~~~~~

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