Submission #30484

#	Time	Username	Problem	Language	Result	Execution time	Memory
30484		sampriti	Network (BOI15_net)	C++14	100 / 100	783 ms	41660 KiB

net

#include <cstdio>
#include <algorithm>
#include <vector>
#include <cassert>

using namespace std;

vector<int> G[500001];
vector<int> leaves;

void dfs(int i, int p) {
  if(G[i].size() == 1) leaves.push_back(i);

  for(int j = 0; j < G[i].size(); j++) {
    int u = G[i][j];
    if(u == p) continue;
    dfs(u, i);
  }
}

int main() {
  int N; scanf("%d", &N);

  for(int i = 0; i < N - 1; i++) {
    int a, b; scanf("%d %d", &a, &b);
    G[a].push_back(b);
    G[b].push_back(a);
  }

  dfs(1, 0);

  int ans = (leaves.size() + 1)/2;

  printf("%d\n", ans);

  for(int i = 0; i < ans; i++) {
    assert((i + leaves.size()/2) < leaves.size());
    printf("%d %d\n", leaves[i], leaves[i + leaves.size()/2]);
  }
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int, int)':
net.cpp:14:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j = 0; j < G[i].size(); j++) {
                    ^
net.cpp: In function 'int main()':
net.cpp:22:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   int N; scanf("%d", &N);
                         ^
net.cpp:25:37: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int a, b; scanf("%d %d", &a, &b);
                                     ^

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