Submission #289023

#	Time	Username	Problem	Language	Result	Execution time	Memory
289023		evpipis	Mousetrap (CEOI17_mousetrap)	C++11	45 / 100	911 ms	79868 KiB

mousetrap

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

#define fi first
#define se second
#define mp make_pair
#define pb push_back
typedef pair<int, int> ii;

const int len = 1e6+5, inf = 1e9;
vector<int> adj[len], cost[len], order;
int block[len], dp[2][len];

int fix_order(int u, int p, int en){
    if (u == en){
        block[u] = 1;
        return 1;
    }

    for (auto v: adj[u]){
        if (v == p) continue;

        if (fix_order(v, u, en)){
            order.pb(u);
            block[u] = 1;
            return 1;
        }
    }

    return 0;
}

int run_dfs(int u, int p){
    int mx1 = 0, mx2 = 0, kids = 0;
    for (auto v: adj[u]){
        if (v == p) continue;

        kids++;

        int cur = run_dfs(v, u);
        if (cur > mx1)
            mx2 = mx1, mx1 = cur;
        else if (cur > mx2)
            mx2 = cur;
    }

    return mx2+kids;
}

int main(){
    int n, en, st;
    scanf("%d %d %d", &n, &en, &st);
    for (int i = 0; i < n-1; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        adj[a].pb(b);
        adj[b].pb(a);
    }


    fix_order(st, st, en);
    reverse(order.begin(), order.end());

    for (int i = (int)order.size()-1, cnt = 0; i >= 0; i--){
        int u = order[i];

        //printf("i = %d, u = %d\n", i, u);
        for (auto v: adj[u]){
            if (block[v]) continue;

            cost[i].pb(run_dfs(v, u)+1);

            //printf("%d -> %d, cost = %d\n", u, v, cost[i].back());
        }

        sort(cost[i].begin(), cost[i].end());
        reverse(cost[i].begin(), cost[i].end());

        for (int j = (int)cost[i].size()-1; j >= 0; j--)
            cost[i][j] += cnt++;
    }

    for (int i = (int)order.size()-1; i >= 0; i--){
        for (int rem = 1; rem <= i+1; rem++){
            dp[i&1][rem] = inf;
            if (rem >= cost[i].size())
                dp[i&1][rem] = cost[i].size() + dp[(i+1)&1][rem-cost[i].size()+1];

            int opt = -1;
            for (int j = 0; j < cost[i].size(); j++){
                if (j <= rem && cost[i][j] >= dp[(i+1)&1][rem-j+1])
                    opt = j;
                //if (j <= rem)
                  //  dp[i&1][rem] = min(dp[i&1][rem], j+max(cost[i][j], dp[(i+1)&1][rem-j+1]));
            }

            if (opt != -1)
                dp[i&1][rem] = min(dp[i&1][rem], opt + cost[i][opt]);
            else
                dp[i&1][rem] = min(dp[i&1][rem], dp[(i+1)&1][rem+1]);
        }
    }

    printf("%d\n", dp[0][1]);
    return 0;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:86:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   86 |             if (rem >= cost[i].size())
      |                 ~~~~^~~~~~~~~~~~~~~~~
mousetrap.cpp:90:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   90 |             for (int j = 0; j < cost[i].size(); j++){
      |                             ~~^~~~~~~~~~~~~~~~
mousetrap.cpp:52:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   52 |     scanf("%d %d %d", &n, &en, &st);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:55:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   55 |         scanf("%d %d", &a, &b);
      |         ~~~~~^~~~~~~~~~~~~~~~~

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