Submission #106891

#	Time	Username	Problem	Language	Result	Execution time	Memory
106891		Pajaraja	Network (BOI15_net)	C++17	100 / 100	735 ms	47688 KiB

net

#include <bits/stdc++.h>
using namespace std;
vector<int> g[500007];
int k[500007],cnt;
void dfs(int s,int f)
{
    if(g[s].size()==1) {k[cnt++]=s; return;}
    for(int i=0;i<g[s].size();i++) if(g[s][i]!=f) dfs(g[s][i],s);
}
int main()
{
    int n,v1,v2,l=0;
    scanf("%d",&n);
    for(int i=0;i<n-1;i++)
    {
        scanf("%d%d",&v1,&v2);
        g[v1].push_back(v2);
        g[v2].push_back(v1);
    }
    for(int i=1;i<=n;i++) if(g[i].size()==1) l++;
    printf("%d\n",(l+1)/2);
    for(int i=1;i<=n;i++) if(g[i].size()>1)
    {
        dfs(i,0);
      	for(int j=0;j<l/2;j++) printf("%d %d\n",k[j],k[j+(l+1)/2]);
      	if(l%2==1) printf("%d %d",i,k[l/2]);
        return 0;
    }
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int, int)':
net.cpp:8:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<g[s].size();i++) if(g[s][i]!=f) dfs(g[s][i],s);
                 ~^~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:13:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
net.cpp:16:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&v1,&v2);
         ~~~~~^~~~~~~~~~~~~~~~

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