Submission #1002357

#	Time	Username	Problem	Language	Result	Execution time	Memory
1002357		GrindMachine	Beads and wires (APIO14_beads)	C++17	57 / 100	1053 ms	28764 KiB

beads

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
 
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
 
template<typename T>
void amin(T &a, T b) {
    a = min(a,b);
}
 
template<typename T>
void amax(T &a, T b) {
    a = max(a,b);
}
 
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
 
/*
 
read some solution ideas, found them non-intuitive 
trying to build upon my previous idea 

*/
 
const int MOD = 1e9 + 7;
const int N = 2e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
 
vector<pii> adj[N];
vector<int> dp[N];
vector<int> best(N,-inf1);

void dfs1(ll u, ll p){
    for(auto [v,w] : adj[u]){
        if(v == p) conts;
        dfs1(v,u);
    }
    
    dp[u][0] = 0;
    int sum = 0;
 
    rep(i,sz(adj[u])){
        auto [v,w] = adj[u][i];
        if(v == p) conts;
        int curr_val = max(w+best[v],dp[v][0]);
        dp[u][0] += curr_val;     
        dp[u][i+1] = -curr_val;
    }
    
    rep1(i,sz(adj[u])){
        dp[u][i] += dp[u][0];
    }

    best[u] = -inf1;
    rep(j,sz(adj[u])){
        auto [v,w] = adj[u][j];
        if(v == p) conts;
        amax(best[u],w+dp[u][j+1]+dp[v][0]);
    }
}

int ans = 0;

void dfs2(int u, int p){
    amax(ans,dp[u][0]);
    // debug(u,dp[u][0]);

    rep(i,sz(adj[u])){
        auto [v,w] = adj[u][i];
        if(v == p) conts;

        int id = -1;
        rep(j,sz(adj[v])){
            auto [v2,w2] = adj[v][j];
            if(v2 == u){
                id = j+1;
                break;
            }
        }

        int contrib = max(w+best[v],dp[v][0]);
        dp[u][i+1] += contrib;
        rep(j,sz(adj[u])+1){
            dp[u][j] -= contrib;
        }

        int add = 0;

        rep(j,sz(adj[u])){
            if(j == i) conts;
            auto [v2,w2] = adj[u][j];
            int val = w+w2+dp[u][j+1]+dp[v2][0];
            amax(add,val);
        }

        amax(add,dp[u][0]);

        dp[v][id] -= add;
        rep(j,sz(adj[v])+1){
            dp[v][j] += add;
        }

        dfs2(v,u);

        rep(j,sz(adj[u])+1){
            dp[u][j] += contrib;
        }
        dp[u][i+1] -= contrib;

        rep(j,sz(adj[v])+1){
            dp[v][j] -= add;
        }
        dp[v][id] += add;
    }
}

void solve(int test_case)
{
    int n; cin >> n;
    rep1(i,n-1){
        int u,v,c; cin >> u >> v >> c;
        adj[u].pb({v,c}), adj[v].pb({u,c});
    }
    
    rep1(u,n){
        dp[u] = vector<int>(sz(adj[u])+1);
    }

    dfs1(1,-1);
    dfs2(1,-1);

    cout << ans << endl;

    // int oans = 0;
    // rep1(i,n){
    //     dfs1(i,-1);
    //     amax(oans,dp[i][0]);
    //     debug(dp[i][0]);
    // }

    // assert(ans == oans);
}
 
int main()
{
    fastio;
 
    int t = 1;
    // cin >> t;
 
    rep1(i, t) {
        solve(i);
    }
 
    return 0;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs1(ll, ll)':
beads.cpp:72:9: warning: unused variable 'sum' [-Wunused-variable]
   72 |     int sum = 0;
      |         ^~~

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 0 / 43