Submission #776490

#	Time	Username	Problem	Language	Result	Execution time	Memory
776490		horiiseun	Network (BOI15_net)	C++17	63 / 100	3 ms	5204 KiB

net

#include <iostream>
#include <vector>
#include <tuple>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <map>
#include <cmath>
#include <random>
#include <string>
#include <bitset>
#include <cassert>
#include <climits>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>
using namespace std;
 
#define ll long long
#define f first
#define s second
 
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
 
template<typename A> void __print(const A &x);
template<typename A, typename B> void __print(const pair<A, B> &p);
template<typename... A> void __print(const tuple<A...> &t);
template<typename T> void __print(stack<T> s);
template<typename T> void __print(queue<T> q);
template<typename T, typename... U> void __print(priority_queue<T, U...> q);
 
template<typename A> void __print(const A &x) {
    bool first = true;
    cerr << '{';
    for (const auto &i : x) {
        cerr << (first ? "" : ","), __print(i);
        first = false;
    }
    cerr << '}';
}
 
template<typename A, typename B> void __print(const pair<A, B> &p) {
    cerr << '(';
    __print(p.f);
    cerr << ',';
    __print(p.s);
    cerr << ')';
}
 
template<typename... A> void __print(const tuple<A...> &t) {
    bool first = true;
    cerr << '(';
    apply([&first] (const auto &...args) { ((cerr << (first ? "" : ","), __print(args), first = false), ...); }, t);
    cerr << ')';
}
 
template<typename T> void __print(stack<T> s) {
    vector<T> debugVector;
    while (!s.empty()) {
        T t = s.top();
        debugVector.push_back(t);
        s.pop();
    }
    reverse(debugVector.begin(), debugVector.end());
    __print(debugVector);
}
 
template<typename T> void __print(queue<T> q) {
    vector<T> debugVector;
    while (!q.empty()) {
        T t = q.front();
        debugVector.push_back(t);
        q.pop();
    }
    __print(debugVector);
}
 
template<typename T, typename... U> void __print(priority_queue<T, U...> q) {
    vector<T> debugVector;
    while (!q.empty()) {
        T t = q.top();
        debugVector.push_back(t);
        q.pop();
    }
    __print(debugVector);
}
 
void _print() { cerr << "]\n"; }
 
template <typename Head, typename... Tail> void _print(const Head &H, const Tail &...T) {
    __print(H);
    if (sizeof...(T)) cerr << ", ";
    _print(T...);
}
 
#ifdef DEBUG
	#define D(...) cerr << "Line: " << __LINE__ << " [" << #__VA_ARGS__ << "] = ["; _print(__VA_ARGS__)
#else
    #define D(...)
#endif

int n, deg[100005], rt, idx, in[100005];
vector<int> adj[100005];
vector<pair<int, int>> leaf, ret;

void dfs(int curr, int par) {
    in[curr] = idx++;
    for (int i : adj[curr]) {
        if (i == par) continue;
        dfs(i, curr);
    }
}

int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(0);

    cin >> n;
    for (int i = 0, a, b; i < n - 1; i++) {
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
        deg[a]++;
        deg[b]++;
    }

    for (int i = 1; i <= n; i++) {
        if (deg[i] > 1) {
            rt = i;
            break;
        }
    }

    dfs(rt, -1);

    for (int i = 1; i <= n; i++) {
        if (deg[i] == 1) {
            leaf.push_back({in[i], i});
        }
    }
    sort(leaf.begin(), leaf.end());
    
    for (int i = 0; i < leaf.size() / 2; i++) {
        ret.push_back({leaf[i].s, leaf[i + leaf.size() / 2].s});
    }
    if (leaf.size() % 2) ret.push_back({leaf.back().s, leaf[0].s});

    cout << ret.size() << "\n";
    for (auto [a, b] : ret) {
        cout << a << " " << b << "\n";
    }

}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:157:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  157 |     for (int i = 0; i < leaf.size() / 2; i++) {
      |                     ~~^~~~~~~~~~~~~~~~~

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