Submission #289264

#	Time	Username	Problem	Language	Result	Execution time	Memory
289264		evpipis	Mousetrap (CEOI17_mousetrap)	C++11	100 / 100	944 ms	170744 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;
}

bool can_win(int x){
    int used = 0;
    for (int i = 0; i < (int)order.size(); i++){
        for (int j = 0; j < cost[i].size(); j++){
            if (cost[i][j]+used > x && used == i+1)
                return false;

            if (cost[i][j]+used > x)
                used++;
        }
    }

    if (used > x)
        return false;
    return true;
}

int bs(int l, int r){
    int ans;
    while (l <= r){
        int mid = (l+r)/2;
        if (can_win(mid))
            ans = mid, r = mid-1;
        else
            l = mid+1;
    }

    return ans;
}

int main(){
    //freopen("trap.01.05.in", "r", stdin);

    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++;

        /*printf("i = %d\n", i);
        for (int j = 0; j < cost[i].size(); j++)
            printf("%d ", cost[i][j]);
        printf("\n");*/
    }

    //printf("and answer is\n");
    printf("%d\n", bs(0, n));
    return 0;
}

Compilation message (stderr)

mousetrap.cpp: In function 'bool can_win(int)':
mousetrap.cpp:53:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   53 |         for (int j = 0; j < cost[i].size(); j++){
      |                         ~~^~~~~~~~~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:84:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   84 |     scanf("%d %d %d", &n, &en, &st);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
mousetrap.cpp:87:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   87 |         scanf("%d %d", &a, &b);
      |         ~~~~~^~~~~~~~~~~~~~~~~
mousetrap.cpp: In function 'int bs(int, int)':
mousetrap.cpp:77:12: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
   77 |     return ans;
      |            ^~~

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