제출 #791780

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
791780		phoebe	Islands (IOI08_islands)	C++17	90 / 100	596 ms	131072 KiB

islands

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

// #define int long long
#define ll long long
#define pii pair<ll, int>
#define F first
#define S second
#define PB push_back
#define ALL(x) x.begin(), x.end()
#define FOR(i, n) for (int i = 0; i < n; i++)
#define NYOOM ios::sync_with_stdio(0); cin.tie(0);
#define endl '\n'
const int INF = 1e9 + 7;
const ll LLINF = 1ll<<60;

const int maxn = 1e6 + 10;
int n, p[maxn], l[maxn], seen[maxn] = {0}; // 0 = unseen, 1 = seeing, 2 = seen
ll val[maxn], cur = 0, re = 0; // val[v][i] = node v connected to i nodes already
// val[v][2] >= val[v][1] >= val[v][0]
bool on_cycle[maxn] = {0};
vector<int> adj[maxn];

void dfs(int v, int p){
    val[v] = 0;
    ll best = -1, second_best = -1;
    for (auto u : adj[v]){
        if (on_cycle[u] || u == p) continue;
        dfs(u, v);
        val[v] = max(val[v], val[u] + l[u]);
        if (best == -1) best = val[u] + l[u];
        else second_best = max(second_best, val[u] + l[u]);
        if (second_best > best) swap(best, second_best);
    }
    cur = max(cur, best + second_best);
}

void solve(int s, int sz, ll total_sum){
    int v = s;
    // forward
    ll cw = -LLINF, ccw = -LLINF, cur_sum = 0;
    FOR(i, sz){
        cur = max(cur, cw + val[v] + cur_sum);
        cur = max(cur, ccw + val[v] + (total_sum - cur_sum));
        cw = max(cw, val[v] - cur_sum);
        ccw = max(ccw, val[v] + cur_sum);
        cur_sum += l[v]; v = p[v];
    }
}

void find_cycle(int s){
    int v = s; 
    while (seen[v] == 0){ // while unseen
        seen[v] = 1; v = p[v];
    }
    if (seen[v] == 1){ // found a cycle
        cur = 0; int sz = 0; ll total_sum = 0;
        while (!on_cycle[v]){
            total_sum += l[v];
            sz++; on_cycle[v] = true; v = p[v];
        }
        FOR(i, sz){
            dfs(v, v); v = p[v];
        }
        solve(v, sz, total_sum);
        re += cur;
    }
    v = s; 
    while (seen[v] != 2){
        seen[v] = 2; v = p[v];
    }
}

signed main(){
    NYOOM;
    // freopen("isl.in", "r", stdin);
    // freopen("isl.out", "w", stdout);
    cin >> n;
    for (int i = 1; i <= n; i++){
        cin >> p[i] >> l[i];
        adj[p[i]].PB(i);
    }
    for (int i = 1; i <= n; i++){
        if (seen[i] != 2) find_cycle(i);
    }
    cout << re;
}

• 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