Submission #1058777

#	Time	Username	Problem	Language	Result	Execution time	Memory
1058777		gyg	Cat in a tree (BOI17_catinatree)	C++17	51 / 100	187 ms	107552 KiB

catinatree

#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1500 + 5, INF = 1e9;
 
int n, d;
array<vector<int>, MAX_N> adj;
 
array<array<int, MAX_N>, MAX_N> dist;
array<bool, MAX_N> seen;
void dfs(int u, int orig, int d = 0) {
    seen[u] = true, dist[orig][u] = d;
    for (int v : adj[u])
        if (!seen[v]) dfs(v, orig, d + 1);
}
void precomp() {
    for (int u = 1; u <= n; u++) {
        fill(seen.begin(), seen.end(), false);
        dfs(u, u);
    }
}
 
array<unordered_set<int>, MAX_N> range;
array<bool, MAX_N> del;
int comp() {
    for (int u = 1; u <= n; u++)
        for (int v = 1; v <= n; v++)
            if (dist[u][v] < d) range[u].insert(v);
    
    int ans = 0;
    while (true) {
        int min_siz = INF, best = -1;
        for (int u = 1; u <= n; u++) {
            if (del[u]) continue;
            if (range[u].size() >= min_siz) continue;
            min_siz = range[u].size(), best = u;
        }
        if (best == -1) break;
 
        ans++;
        for (int u : range[best]) del[u] = true;
        for (int u = 1; u <= n; u++) {
            if (del[u]) continue;
            vector<int> to_del;
            for (int v : range[u])
                if (del[v]) to_del.push_back(v);
            for (int v : to_del) range[u].erase(v);
        }
    }
    return ans;
}
 
int main() {
    // freopen("cat.in", "r", stdin);
    cin >> n >> d; assert(n <= 1500);
    for (int u = 2; u <= n; u++) {
        int v; cin >> v; v++;
        adj[u].push_back(v), adj[v].push_back(u);
    }
 
    precomp();
    int ans = comp();
    cout << ans << '\n';
}

Compilation message (stderr)

catinatree.cpp: In function 'int comp()':
catinatree.cpp:34:33: warning: comparison of integer expressions of different signedness: 'std::unordered_set<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   34 |             if (range[u].size() >= min_siz) continue;
      |                 ~~~~~~~~~~~~~~~~^~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 40 / 40
• Subtask 3: 0 / 49