Submission #59750

#	Time	Username	Problem	Language	Result	Execution time	Memory
59750		Benq	Beads and wires (APIO14_beads)	C++11	100 / 100	394 ms	32032 KiB

beads

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
 
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
 
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
 
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
 
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
 
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
 
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 200001;
 
int n, ans;
vpi adj[MX];
pi ret[MX], oops[MX];

vpi genPre(vector<array<int,3>> v) {
    vpi V;
    int fst = 0, mx = -MOD;
    for (auto a: v) {
        fst += max(a[0],a[1]+a[2]);
        mx = max(mx,a[0]+a[2]-max(a[0],a[1]+a[2]));
        V.pb({fst,mx});
    }
    return V;
}

pi eval(vector<array<int,3>> v) {
    if (sz(v) == 0) return {0,-MOD};
    pi a = genPre(v).back(); a.s += a.f;
    return a;
}

void dfs(int cur, int pre) {
    vector<array<int,3>> v;
    for (auto a: adj[cur]) if (a.f != pre) {
        dfs(a.f,cur); 
        v.pb({ret[a.f].f,ret[a.f].s,a.s});
    }
    ret[cur] = eval(v);
}
 
vpi genSuf(vector<array<int,3>> v) {
    reverse(all(v));
    auto a = genPre(v);
    reverse(all(a));
    return a;
}

void dfs2(int cur, int pre) {
    vector<array<int,3>> v;
    for (auto a: adj[cur]) {
        if (a.f != pre) v.pb({ret[a.f].f,ret[a.f].s,a.s});
        else v.pb({oops[cur].f,oops[cur].s,a.s});
    }
    
    vpi L = genPre(v), R = genSuf(v);
    
    ans = max(ans,L.back().f);
    // if (cur == 1) cout << "HI " << ans << "\n";
    
    int i = 0;
    for (auto a: adj[cur]) {
        if (a.f != pre) {
            oops[a.f].f = (i == 0 ? 0 : L[i-1].f)+(i == sz(R)-1 ? 0 : R[i+1].f);
            oops[a.f].s = oops[a.f].f+max(i == 0 ? -MOD : L[i-1].s,i == sz(R)-1 ? -MOD : R[i+1].s);
            dfs2(a.f,cur);
        }
        i ++;
    }
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin >> n;
    F0R(i,n-1) {
        int a,b,c; cin >> a >> b >> c;
        adj[a].pb({b,c}), adj[b].pb({a,c});
    }
    dfs(1,0);
    dfs2(1,0);
    cout << ans;
}
 
/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( ) 
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/

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