Submission #716228

#	Time	Username	Problem	Language	Result	Execution time	Memory
716228		socpite	Mousetrap (CEOI17_mousetrap)	C++14	100 / 100	1010 ms	182124 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];
vector<int> path;

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;
        }
    }
    if(onp[x] && x != t)path.push_back(x);
    //cout << x << " " << dp[x] << endl;
}

void dfs(int x, int p){
    if(x == t)return;
    vector<int> val;
    for(auto v: g[x]){
        if(v == p)continue;
        dfs(v, x);
        val.push_back(dp[v]);
    }
    if(val.empty())dp[x] = 0;
    else if(val.size() == 1)dp[x] = 1;
    else{
        sort(val.begin(), val.end());
        dp[x] = val[val.size()-2] + val.size();
    }
}

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

bool chk(){
    int used = 0, cap = 0;
    for(auto x: path){
        cap++;
        int last = used;
        for(auto v: g[x]){
            if(onp[v])continue;
            if(dp[v] + last > mid)used++;
        }
        //cout << used << endl;
        if(used > cap)return 0;
    }
    return used <= mid;
}


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);
    reverse(path.begin(), path.end());
    for(auto x: path){
        for(auto v: g[x])if(!onp[v])dfs(v, x);
    }
    dfs2(m, 0);
    int l = 0, r = 2*maxn;
    while(l < r){
        mid = (l+r)>>1;
        if(chk())r = mid;
        else l = mid+1;
    }
    cout << l;
}

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