Submission #1202742

#	Time	Username	Problem	Language	Result	Execution time	Memory
1202742		Zbyszek99	Beads and wires (APIO14_beads)	C++20	100 / 100	69 ms	17848 KiB

beads

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;

vector<pii> graph[200001];
int dp[200001][2];
int ans = 0;

void dfs(int v, int pop, int pop_edge)
{
    int sum = 0;
    int best_son = -5e8;
    forall(it,graph[v])
    {
        if(it.ff != pop)
        {
            dfs(it.ff,v,it.ss);
            sum += max(dp[it.ff][0],dp[it.ff][1]);
            best_son = max(best_son,dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1]));
        }
    }
    dp[v][0] = sum;
    dp[v][1] = sum + best_son + pop_edge;
}

void dfs_ans(int v, int pop)
{
    int old_dp0 = dp[v][0];
    int old_dp1 = dp[v][1];
    int sum = 0;
    pii best_son = {-5e8,-5e8};
    forall(it,graph[v])
    {
        sum += max(dp[it.ff][0],dp[it.ff][1]);
        if(best_son.ff < dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1]))
        {
            best_son.ss = best_son.ff;
            best_son.ff = dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1]);
        }
        else if(best_son.ss < dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1]))
        {
            best_son.ss = dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1]);
        }
    }
   // cout << v << " " << sum << " " << best_son.ff << " " << best_son.ss << " dfs\n";
    ans = max(ans,sum);
    forall(it,graph[v])
    {
        if(it.ff != pop)
        {
            dp[v][0] = sum - max(dp[it.ff][0],dp[it.ff][1]);
            int b = best_son.ff;
            if(b == dp[it.ff][0] + it.ss - max(dp[it.ff][0],dp[it.ff][1])) b = best_son.ss;
            dp[v][1] = sum + b + it.ss - max(dp[it.ff][0],dp[it.ff][1]);
            dfs_ans(it.ff,v);
        }
    }
    dp[v][0] = old_dp0;
    dp[v][1] = old_dp1;
}

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    //random_start();
    int n;
    cin >> n;
    rep(i,n-1)
    {
        int a,b,c;
        cin >> a >> b >> c;
        graph[a].pb({b,c});
        graph[b].pb({a,c});
    }
    dfs(1,1,0);
    dfs_ans(1,1);
    cout << ans << "\n";
}

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 43 / 43