Submission #1248978

#	Time	Username	Problem	Language	Result	Execution time	Memory
1248978		anha3k25cvp	Forensic (NOI12_forensic)	C++20	25 / 25	2 ms	2372 KiB

forensic

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define dl double
#define st first
#define nd second
#define II pair <int, int>

using namespace std;

const int N = 5 + 1e5;
const int inf = 7 + 1e9;

int node = 0;
vector <int> a, f, num, low, vis;

void dfs(int u) {
    vis[u] = 1;
    num[u] = low[u] = ++ node;
    int v = a[u];
    if (v < 0) {
        f[u] = 1;
        vis[u] = 2;
        return;
    }
    if (!num[v])
        dfs(v);
    low[u] = min(low[u], low[v]);
    if (vis[v] == 1)
        f[u] = -1;
    else
        f[u] = f[v] + (f[v] < 0 ? 0 : 1);
    vis[u] = 2;
}

int main() {
#define TASKNAME ""
    ios_base :: sync_with_stdio (0);
    cin.tie (0);
    if ( fopen( TASKNAME".inp", "r" ) ) {
        freopen (TASKNAME".inp", "r", stdin);
        freopen (TASKNAME".out", "w", stdout);
    }
    int n;
    cin >> n;
    a.assign(n, 0);
    vector <int> deg(n + 1, 0);
    for (int i = 0; i < n; i ++) {
        cin >> a[i];
        if (a[i] >= 0)
            deg[a[i]] ++;
    }
    f.assign(n, -1);
    num.assign(n, 0);
    low.assign(n, 0);
    vis.assign(n, 0);
    for (int i = 0; i < n; i ++)
        if (!deg[i] || i == 0)
            dfs(i);
    vector <int> suf(n + 2, 0);
    for (int i = 0; i < n; i ++)
        suf[low[i]] = max(suf[low[i]], f[i]);
    for (int i = n; i >= 1; i --)
        suf[i] = max(suf[i], suf[i + 1]);
    int u = 0, last = 1, ans = 0;
    while (1) {
        ans = max(ans, num[u] + suf[num[u] + 1]);
        if (a[u] < 0)
            break;
        u = a[u];
        if (num[u] <= last)
            break;
        last = num[u];
    }
    cout << ans;
    return 0;
}

Compilation message (stderr)

forensic.cpp: In function 'int main()':
forensic.cpp:41:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   41 |         freopen (TASKNAME".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
forensic.cpp:42:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   42 |         freopen (TASKNAME".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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