Submission #973817

#	Time	Username	Problem	Language	Result	Execution time	Memory
973817		GrindMachine	Islands (IOI08_islands)	C++17	90 / 100	1010 ms	131072 KiB

islands

#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

/*



*/

const int MOD = 1e9 + 7;
const int N = 1e6 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

vector<pii> adj[N];
vector<bool> on_cyc(N,1);
vector<ll> mxd(N);

void dfs1(ll u, ll p){
    for(auto [v,w] : adj[u]){
        if(v == p or on_cyc[v]) conts;
        dfs1(v,u);
        amax(mxd[u],mxd[v]+w);
    }
}

pll diam;

void dfs2(ll u, ll p, ll d){
    pll px = {d,u};
    amax(diam,px);
    for(auto [v,w] : adj[u]){
        if(v == p or on_cyc[v]) conts;
        dfs2(v,u,d+w);
    }
}

void solve(int test_case)
{
    int n; cin >> n;
    vector<int> a(n+5), b(n+5);
    rep1(u,n){
        int v,w; cin >> v >> w;
        a[u] = v;
        b[u] = w;
        adj[u].pb({v,w}), adj[v].pb({u,w});
    }

    queue<int> q;
    vector<int> indeg(n+5);
    rep1(i,n) indeg[a[i]]++;
    rep1(i,n){
        if(!indeg[i]){
            q.push(i);
        }
    }

    while(!q.empty()){
        int u = q.front();
        q.pop();
        on_cyc[u] = 0;
        int v = a[u];
        indeg[v]--;
        if(!indeg[v]){
            q.push(v);
        }
    }

    vector<bool> vis(n+5);
    ll ans = 0;

    rep1(i,n){
        if(!on_cyc[i]) conts;
        if(vis[i]) conts;
        
        int j = i;
        vector<pii> nodes;
        vector<int> weights;
        while(!vis[j]){
            vis[j] = 1;
            nodes.pb({j,-1});
            weights.pb(b[j]);
            j = a[j];
        }

        int siz = sz(nodes);
        rep(j,siz){
            nodes[j].ss = weights[(j-1+siz)%siz];
        }

        vector<ll> p(siz);
        rep(j,siz){
            p[j] = nodes[j].ss;
            if(j) p[j] += p[j-1]; 
        }
        ll len = p.back();
        ll best = 0, mx1 = -inf2, mx2 = -inf2;

        rep(j,siz){
            int u = nodes[j].ff;
            dfs1(u,-1);
            ll d = mxd[u];
            amax(best,d+p[j]+mx1);
            amax(best,d-p[j]+mx2+len);
            amax(mx1,d-p[j]);
            amax(mx2,d+p[j]);

            on_cyc[u] = 0;
            diam = {-1,-1};
            dfs2(u,-1,0);
            ll s = diam.ss;
            diam = {-1,-1};
            dfs2(s,-1,0);
            amax(best,diam.ff);
            on_cyc[u] = 1;
        }

        ans += best;
    }

    cout << ans << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;

    rep1(i, t) {
        solve(i);
    }

    return 0;
}

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 0 / 10