Submission #79598

#	Time	Username	Problem	Language	Result	Execution time	Memory
79598		EntityIT	Network (BOI15_net)	C++14	0 / 100	14 ms	12152 KiB

net

#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;
vector<int> gr[N], vec;

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

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

void dfs (int u, int p) {
    for (int v : gr[u]) if (v != p) dfs(v, u);
    if (gr[u].size() == 1) vec.pb(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);
    cout << (nLeaf + 1) / 2 << '\n';
    prep(1, 1);
    int cen = findCentroid(1, 1);

    for (int u : gr[cen]) dfs(u, cen);

    for (int i = 0; i < vec.size() - (nLeaf + 1) / 2; ++i) {
        cout << vec[i] << ' ' << vec[ i + (nLeaf + 1) / 2 ] << '\n';
    }

    if (nLeaf % 2) cout << vec[0] << ' ' << vec[nLeaf / 2];

    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:49:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < vec.size() - (nLeaf + 1) / 2; ++i) {
                     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37