Submission #297206

#	Time	Username	Problem	Language	Result	Execution time	Memory
297206		PeppaPig	Network (BOI15_net)	C++14	100 / 100	581 ms	47732 KiB

net

#include <bits/stdc++.h>

using namespace std;

const int N = 5e5 + 5;

int n;
vector<int> g[N], ans;

void dfs(int u, int p) {
	if(g[u].size() == 1) ans.emplace_back(u);
	for(int v : g[u]) if(v != p)
		dfs(v, u);
}

int main() {
	scanf("%d", &n);
	for(int i = 1, a, b; i < n; i++) {
		scanf("%d %d", &a, &b);
		g[a].emplace_back(b);
		g[b].emplace_back(a);
	}
	for(int i = 1; i <= n; i++) if(g[i].size() != 1) {
		dfs(i, 0);
		break;
	}
	
	printf("%d\n", (ans.size() + 1) / 2);
	for(int i = 0; i < ans.size() / 2; i++)
		printf("%d %d\n", ans[i], ans[ans.size() / 2 + i]);
	if(ans.size() & 1)
		printf("%d %d\n", ans[0], ans.back());

	return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:28:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wformat=]
   28 |  printf("%d\n", (ans.size() + 1) / 2);
      |          ~^     ~~~~~~~~~~~~~~~~~~~~
      |           |                      |
      |           int                    std::vector<int>::size_type {aka long unsigned int}
      |          %ld
net.cpp:29:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |  for(int i = 0; i < ans.size() / 2; i++)
      |                 ~~^~~~~~~~~~~~~~~~
net.cpp:17:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   17 |  scanf("%d", &n);
      |  ~~~~~^~~~~~~~~~
net.cpp:19:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   19 |   scanf("%d %d", &a, &b);
      |   ~~~~~^~~~~~~~~~~~~~~~~

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