Submission #525106

#	Time	Username	Problem	Language	Result	Execution time	Memory
525106		benedict0724	Firefighting (NOI20_firefighting)	C++17	3 / 100	266 ms	25544 KiB

Firefighting

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<int, ll> pi;
const ll INF = 1e18;
int n; ll k;

vector<pi> adj[300002];
bool chk[300002];
int ans = 0;

ll dfs(int x, int p, ll d)
{
    vector<ll> v;
    ll tmp1 = INF, tmp2 = 0;
    ll D = INF; int t = 1;
    for(auto u : adj[x])
    {
        int i = u.first;
        if(i == p) continue;
        ll c = u.second;
        ll P = dfs(i, x, c);
        if(P > 0 && P < tmp1)
        {
            tmp1 = P;
            t = 1;
        }
        if(P < 0 && -P > tmp2)
        {
            tmp2 = -P;
            t = -1;
        }
    }

    if(tmp1 == INF && tmp2 == 0) { D = INF; }
    else if(tmp1 == INF) { D = tmp2; t = -1; }
    else if(tmp1 > tmp2) { D = tmp1; t = 1; }
    else { D = tmp2; t = -1; }

    if(D == INF)
    {
        if(d > k)
        {
            chk[x] = 1; ans++;
            return 2*k+2;
        }
        return -(d+k+1);
    }

    if(D > k && D + d > 2*k+1)
    {
        chk[x] = 1; ans++;
        return min(d, k+1);
    }
    else if(D > k) return t*(D+d);
    if(D + d > k) return t*(k+1);
    else return t*(D+d);
}

int main()
{
    ios::sync_with_stdio(false); cin.tie(NULL);
    cin >> n >> k;
    for(int i=1;i<n;i++)
    {
        int a, b; ll D; cin >> a >> b >> D;
        adj[a].push_back({b, D});
        adj[b].push_back({a, D});
    }

    ll P = dfs(1, 0, 0);
    if(P <= 0 && chk[1] == 0) { chk[1] = 1; ans++; }
    else if(P > k && chk[1] == 0) { chk[1] = 1; ans++; }

    assert(ans <= n);
    cout << ans << "\n";

    for(int i=1;i<=n;i++) if(chk[i]) cout << i << " ";
}

• Subtask 1: 3 / 3
• Subtask 2: 0 / 5
• Subtask 3: 0 / 9
• Subtask 4: 0 / 19
• Subtask 5: 0 / 26
• Subtask 6: 0 / 38