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Submission #489253

# Submission time Handle Problem Language Result Execution time Memory
489253 2021-11-21T18:26:48 Z dxz05 Islands (IOI08_islands) C++11
90 / 100
 1110 ms 131076 KB 
#pragma GCC optimize("Ofast,O2,O3,unroll-loops")
#pragma GCC target("avx2")

#include <iostream>
#include <vector>
#include <bitset>
#include <stack>
#include <algorithm>
#include <chrono>
#include <random>
using namespace std;

#define SZ(s) ((int)s.size())
#define all(x) (x).begin(), (x).end()
#define lla(x) (x).rbegin(), (x).rend()

#define MP make_pair

typedef long long ll;
const double eps = 0.000001;
const int MOD = 998244353;
const int INF = 1000000101;
const long long LLINF = 1223372000000000555;
const int N = 1e6 + 1;
const int M = 222;

mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());

int f[N], w[N];

int cyc_sz;
int cycle[N];
stack<int> st;
bitset<N> used;

inline void find_cycle(int x){
    while (!st.empty()) st.pop();
    cyc_sz = 0;
    while (true){
        st.push(x);
        used[x] = true;
        if (used[f[x]]){
            while (!st.empty()){
                int y = st.top(); st.pop();
                cycle[cyc_sz++] = y;
                if (y == f[x]) break;
            }
            return;
        }
        x = f[x];
    }
}

int parent[N];
int find(const int x){
    return (x == parent[x] ? x : parent[x] = find(parent[x]));
}

vector<int> g[N];

inline int A(const int &u, const int &v){
    if (f[u] == v && f[v] != u) return w[u];
    if (f[u] != v && f[v] == u) return w[v];
    return max(w[u], w[v]);
}

int X; ll D;

void dfs(const int v, const int p, const ll d, const int c1, const int c2, const bool flag){
    if (d > D) D = d, X = v;
    for (int u : g[v]){
        if (u != p && u != c1 && u != c2) dfs(u, v, d + A(u, v), c1, c2, flag);
    }
    if (flag) g[v].clear();
}

ll arr[N];

inline ll component(const int root){
    find_cycle(root);

    const int n = cyc_sz;

    ll ans = 0;
    for (int i = 0; i < n; i++){
        int v = cycle[i];
        D = -1;
        dfs(v, v, 0, cycle[(i + n - 1) % n], cycle[(i + 1) % n], false);

        ans = max(ans, D);
        arr[v] = D;

        D = -1;
        dfs(X, X, 0, cycle[(i + n - 1) % n], cycle[(i + 1) % n], true);

        ans = max(ans, D);
    }

    if (n == 2){
        int u = cycle[0], v = cycle[1];
        ans = max(ans, arr[u] + arr[v] + A(u, v));
        return ans;
    }

    vector<ll> a(n);
    a[0] = {arr[cycle[0]]};
    ll sum = 0;
    for (int i = 1; i < n; i++){
        sum += A(cycle[i - 1], cycle[i]);
        a[i] = arr[cycle[i]] + sum;
    }
    sum += A(cycle[0], cycle[n - 1]);

    ans = max(ans, arr[cycle[0]] + *max_element(a.begin() + 1, a.end()));

    for (int i = n - 2; i >= 0; i--) a[i] = max(a[i + 1], a[i]);

    ll add = 0;
    int v, u;
    ll mx = 0;
    ll sum2 = 0;
    for (int i = 1; i < n; i++){
        v = cycle[i], u = cycle[i - 1];
        add -= A(v, u);
        mx = max(mx, arr[cycle[i - 1]] + sum2 + sum);

        ans = max(ans, arr[v] + add + mx);
        if (i + 1 < n) ans = max(ans, arr[v] + add + a[i + 1]);
        sum2 += A(v, u);
        mx = max(mx, arr[cycle[i]] + sum2);

    }

    return ans;
}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
    int n;
    cin >> n;

    for (int i = 1; i <= n; i++) parent[i] = i;

    for (int i = 1; i <= n; i++){
        cin >> f[i] >> w[i];
        if (rng() & 1) parent[find(i)] = find(f[i]); else
            parent[find(f[i])] = find(i);
        if (f[f[i]] != i){
            g[i].push_back(f[i]);
            g[f[i]].push_back(i);
        }
    }

    bitset<N> comp;

    ll ans = 0;
    for (int i = 1; i <= n; i++){
        if (!comp[find(i)]){
            comp[find(i)] = true;
            ans += component(i);
        }
    }

    cout << ans;


    return 0;
}

Subtask #1
33.0 / 33.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 23912 KB Output is correct
2 Correct 14 ms 23888 KB Output is correct
3 Correct 14 ms 23880 KB Output is correct
4 Correct 13 ms 23884 KB Output is correct
5 Correct 13 ms 23856 KB Output is correct
6 Correct 13 ms 23884 KB Output is correct
7 Correct 13 ms 23884 KB Output is correct
8 Correct 13 ms 23884 KB Output is correct
9 Correct 12 ms 23884 KB Output is correct
10 Correct 13 ms 23948 KB Output is correct
11 Correct 14 ms 23884 KB Output is correct

Subtask #2
3.0 / 3.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 24012 KB Output is correct
2 Correct 13 ms 24048 KB Output is correct

Subtask #3
4.0 / 4.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 24072 KB Output is correct
2 Correct 15 ms 24168 KB Output is correct

Subtask #4
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 21 ms 24652 KB Output is correct
2 Correct 27 ms 25968 KB Output is correct
3 Correct 22 ms 24992 KB Output is correct
4 Correct 19 ms 24396 KB Output is correct

Subtask #5
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 32 ms 26884 KB Output is correct
2 Correct 47 ms 29332 KB Output is correct

Subtask #6
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 86 ms 34960 KB Output is correct
2 Correct 83 ms 36700 KB Output is correct
3 Correct 101 ms 40324 KB Output is correct

Subtask #7
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 133 ms 44772 KB Output is correct
2 Correct 164 ms 55164 KB Output is correct
3 Correct 194 ms 59576 KB Output is correct
4 Correct 221 ms 65980 KB Output is correct

Subtask #8
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 281 ms 74704 KB Output is correct
2 Correct 773 ms 82188 KB Output is correct
3 Correct 305 ms 65348 KB Output is correct
4 Correct 316 ms 80268 KB Output is correct
5 Correct 339 ms 81172 KB Output is correct
6 Correct 1110 ms 67988 KB Output is correct
7 Correct 335 ms 89876 KB Output is correct

Subtask #9
0 / 10.0

# Verdict Execution time Memory Grader output
1 Runtime error 324 ms 131076 KB Execution killed with signal 9
2 Halted 0 ms 0 KB -