Submission #298510

#	Time	Username	Problem	Language	Result	Execution time	Memory
298510		jbroeksteeg	Network (BOI15_net)	C++14	100 / 100	853 ms	47728 KiB

net

#include <iostream>
#include <climits>
#include <numeric>
#include <cassert>
#include <algorithm>
#include <queue>
#include <map>
#include <stack>
#include <set>
#include <vector>
#include <array>
#include <memory>

#define IN(a,b) (a.find(b) != a.end())
#define p(a,b) make_pair(a,b)
#define readVec(a) for (int __i = 0; __i<(int)a.size();__i++){cin>>a[__i];}

// jimjam

template<typename T>
void pMin(T &a, T b) {if (b<a){a=b;}}
template<typename T>
void pMax(T &a, T b) {if (b>a){a=b;}}
template<typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& c);
template<typename A, typename B>
std::ostream& operator<<(std::ostream& os, const std::pair<A,B>& c) {std::cout << "(" << c.first << ", " << c.second << ")";return os;}
template<typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& c) {
	if (c.size() == 0) {os << "{}"; return os;}
	os << "{" << c[0];
	for (int i = 1; i < (int)c.size(); i++) {os <<", "<<c[i];}
	os << "}";
	return os;
}

const int inf = 2e9;
#define MAXN 500001

using namespace std;

vector<int> adj[MAXN];
vector<int> leaves;

void dfs(int c, int p=-1) {

	if (adj[c].size()==1) {
		leaves.push_back(c);
	}
	for (int i: adj[c]) {
		if (i!=p) {
			dfs(i,c);
		}
	}
}
int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	
	int n; cin >> n;
	for (int i = 0; i < n-1; i++) {
		int a, b; cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	for (int i = 1; i <= n; i++) {
		if (adj[i].size()>1) {
			dfs(i);
			break;
		}
	}
//	cout << leaves.size()/2 + leaves.size()%2 << "\n";
	int cnt=0;
	while (cnt<leaves.size()) {
		if (cnt+1==leaves.size()) {
//			cout << leaves[cnt] << " 1\n";
			cnt++;
		} else {
//			cout << leaves[cnt] << " " << leaves[cnt+1] << "\n";
			cnt+=2;
		}
		
	}
	cout << leaves.size()/2 + leaves.size()%2 << endl;
	for (int i = 0; i < leaves.size()/2+leaves.size()%2; i++) {
		cout << leaves[i] << " " << leaves[i + leaves.size()/2] << endl;
		//if (other<i) break;
	}
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:75:12: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   75 |  while (cnt<leaves.size()) {
      |         ~~~^~~~~~~~~~~~~~
net.cpp:76:12: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   76 |   if (cnt+1==leaves.size()) {
      |       ~~~~~^~~~~~~~~~~~~~~
net.cpp:86:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   86 |  for (int i = 0; i < leaves.size()/2+leaves.size()%2; i++) {
      |                  ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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