Submission #1123248

#	Time	Username	Problem	Language	Result	Execution time	Memory
1123248		kh0i	Forensic (NOI12_forensic)	C++20	25 / 25	2 ms	840 KiB

forensic

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

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...)
#endif

using ll = long long;
using pii = pair<int, int>;

#define F first
#define S second
#define sz(x) (int)((x).size())
#define all(x) (x).begin(), (x).end()

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll get_rand(ll l, ll r) {
    assert(l <= r);
    return uniform_int_distribution<ll> (l, r)(rng);
}

const int N = 20003;

int n, a[N], cnt;
bool vis[N], loop;
int in[N], f[N];

void dfs(int u){
    vis[u] = 1;
    f[u] = 0;
    int v = a[u];
    ++cnt;

    if(v == -1)
        return;
    if(vis[v]){
        loop = 1;
        return;
    }

    dfs(v);
}

int find_path(int u){
    if(u == -1)
        return 0;
    int v = a[u];
    if((loop and vis[v]) or v == 0)
        return -1e9;
    if(f[u] != -1)
        return f[u];
    if(in[u] == 1)
        return -1e9;
    in[u] = 1;
    f[u] = find_path(v) + 1;
    in[u] = 2;
    return f[u];
}

void solve(){
    cin >> n;
    memset(f, -1, sizeof(f));
    for(int i = 0; i < n; ++i)
        cin >> a[i];

    dfs(0);

    int mx = 0;
    for(int i = 0; i < n; ++i)
        if(!vis[i])
            mx = max(mx, find_path(i));
    cout << cnt + mx;
}

int32_t main() {
    cin.tie(nullptr)->sync_with_stdio(0);
    #define task "troll"
    if(fopen(task".inp", "r")){
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    int test = 1;
//    cin >> test;
    for(int i = 1; i <= test; ++i){
//        cout << "Case #" << i << ": ";
        solve();
    }
    #ifdef LOCAL
        cerr << "\n[Time]: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
    #endif
    return 0;
}

Compilation message (stderr)

forensic.cpp: In function 'int32_t main()':
forensic.cpp:81:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   81 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
forensic.cpp:82:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 5 / 5
• Subtask 4: 10 / 10