Submission #752907

#	Time	Username	Problem	Language	Result	Execution time	Memory
752907		benjaminkleyn	Fireworks (APIO16_fireworks)	C++17	7 / 100	4 ms	7392 KiB

fireworks

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

const int MAX = 300010;
int n, m;
int p[2 * MAX]; 
ll c[2 * MAX];
vector<pair<int, ll>> g[MAX];

ll f(vector<ll> &t, ll c)
{
    ll ans = 0;
    for (ll x : t)
        ans += abs(c - x);
    return ans;
}

pair<ll, ll> dp(int u)
{
    if (u > n)
        return {0, 0};
    
    ll res = 0;
    vector<ll> times;
    ll lo = LLONG_MAX, hi = 0;
    for (auto [v, l] : g[u])
    {
        auto [t, d] = dp(v);
        res += t;
        times.push_back(l + d);
        lo = min(lo, l + d);
        hi = max(hi, l + d);
    }

    ll m1, m2;
    while (hi - lo + 1 > 3)
    {
        m1 = lo + (hi - lo) / 3;
        m2 = hi - (hi - lo) / 3;
        if (f(times, m1) < f(times, m2))
            hi = m2;
        else
            lo = m1;
    }

    ll best = lo, cur = LLONG_MAX;
    for (ll c = lo; c <= hi; c++)
    {
        ll maybe = f(times, c);
        if (maybe < cur)
            best = c, cur = maybe;
    }

    for (int i = 0; i < g[u].size(); i++)
        if (times[i] - best > g[u][i].second)
            best = max(best, times[i] - g[u][i].second);
    for (int i = 0; i < g[u].size(); i++)
        res += abs(times[i] - best);
    return {res, best};
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);

    cin >> n >> m;
    p[1] = -1, c[1] = 0;
    for (int i = 2; i <= n + m; i++)
    {
        cin >> p[i] >> c[i];
        g[p[i]].push_back({i, c[i]});
    }

    cout << dp(1).first << '\n';

    return 0;
}

Compilation message (stderr)

fireworks.cpp: In function 'std::pair<long long int, long long int> dp(int)':
fireworks.cpp:55:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |     for (int i = 0; i < g[u].size(); i++)
      |                     ~~^~~~~~~~~~~~~
fireworks.cpp:58:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   58 |     for (int i = 0; i < g[u].size(); i++)
      |                     ~~^~~~~~~~~~~~~

• Subtask 1: 7 / 7
• Subtask 2: 0 / 19
• Subtask 3: 0 / 29
• Subtask 4: 0 / 45