oj.uz

Submission #79558

# Submission time Handle Problem Language Result Execution time Memory
79558 2018-10-15T03:04:26 Z EntityIT Network (BOI15_net) C++14
0 / 100
 13 ms 12288 KB 
#include<bits/stdc++.h>

using namespace std;

#define pb push_back
#define fi first
#define se second
typedef pair<int, int> ii;

const int N = 5e5 + 5;
int n, child[N], nLeaf, cur;
vector<int> gr[N];
set<ii> ver;

void prep (int u, int prev) {
    for (int v : gr[u]) if (v != prev) {
        prep(v, u);
        child[u] += child[v];
    }
    child[u] += (gr[u].size() == 1);
}

int findCentroid (int u, int prev) {
    for (int v : gr[u]) if (v != prev) {
        if (child[v] >= (nLeaf + 1) / 2 ) return findCentroid(v, u);
    }
    return u;
}

void dfs (int u, int prev) {
    for (int v : gr[u]) if (v != prev) dfs(v, u);
    if (gr[u].size() == 1) ver.insert(ii(cur, u) );
}

int main () {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> n;
    for (int _ = 1; _ < n; ++_) {
        int u, v; cin >> u >> v;
        gr[u].pb(v); gr[v].pb(u);
    }

    for (int u = 1; u <= n; ++u) nLeaf += (gr[u].size() == 1);
    prep(1, 1);
    int cen = findCentroid(1, 1);
    for (int u : gr[cen]) cur ++, dfs(u, cen);

    cout << (nLeaf + 1) / 2 << '\n';
    while (ver.size() > 1) {
        cout << (*ver.begin() ).se << ' ' << (*ver.rbegin() ).se << '\n';
        ver.erase(ver.begin() );
        set<ii>::iterator it = ver.end(); it --;
        ver.erase(it);
    }

    if (ver.size() ) cout << cen << ' ' << (*ver.begin() ).se << '\n';

    return 0;
}

Subtask #1
0 / 18.0

# Verdict Execution time Memory Grader output
1 Correct 13 ms 12280 KB Output is correct
2 Incorrect 13 ms 12288 KB Breaking single line is causing network to disconnect.
3 Halted 0 ms 0 KB -

Subtask #2
0 / 45.0

# Verdict Execution time Memory Grader output
1 Correct 13 ms 12280 KB Output is correct
2 Incorrect 13 ms 12288 KB Breaking single line is causing network to disconnect.
3 Halted 0 ms 0 KB -

Subtask #3
0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 13 ms 12280 KB Output is correct
2 Incorrect 13 ms 12288 KB Breaking single line is causing network to disconnect.
3 Halted 0 ms 0 KB -