Submission #305446

#	Time	Username	Problem	Language	Result	Execution time	Memory
305446		shahriarkhan	Network (BOI15_net)	C++14	0 / 100	12 ms	12032 KiB

net

#include<bits/stdc++.h>
using namespace std ;

const int siz = 5e5 + 69 ;

vector<int> adj[siz] ;

int col[siz] ;

void dfs(int s , int p)
{
    for(int t : adj[s])
    {
        if(t==p) continue ;
        dfs(t,s) ;
        col[t] = col[s] ;
    }
}

int main()
{
    int n ;
    scanf("%d",&n) ;
    int deg[n+1] = {0} , mx = 0 , root = 0 ;
    for(int i = 1 ; i < n ; ++i)
    {
        int u , v ;
        scanf("%d%d",&u,&v) ;
        ++deg[u] , ++deg[v] ;
        mx = max(mx,max(deg[u],deg[v])) ;
    }
    for(int i = 1 ; i <= n ; ++i)
    {
        if(deg[i]==mx)
        {
            root = i ;
            break ;
        }
    }
    int cnt = 0 , vis[n+1] = {0} , vi[n+1] = {0} ;
    for(int i : adj[root])
    {
        col[i] = ++cnt ;
        dfs(i,root) ;
    }
    vector<int> ans ;
    for(int i = 1 ; i <= n ; ++i)
    {
        if(deg[i]==1)
        {
            if(!vis[col[i]])
            {
                vi[i] = 1 ;
                vis[col[i]] = 1 ;
                ans.push_back(i) ;
            }
        }
    }
    int p = ans.size() ;
    if(p%2)
    {
        for(int i = 1 ; i <= n ; ++i)
        {
            if(deg[i]==1)
            {
                if(!vi[i])
                {
                    vi[i] = 1 ;
                    ans.push_back(i) ;
                    ++p ;
                    break ;
                }
            }
        }
        if(col[ans[p-2]]==col[ans[p-1]]) swap(ans[p-1],ans[0]) ;
    }
    for(int i = 1 ; i <= n ; ++i)
    {
        if(deg[i]==1)
        {
            if(!vi[i])
            {
                ans.push_back(i) ;
                ++p ;
            }
        }
    }
    if(p%2)
    {
        ans.push_back(ans[p-2]) ;
        ++p ;
    }
    printf("%d\n",p/2) ;
    for(int i = 0 ; i < p ; i += 2)
    {
        printf("%d %d\n",ans[i],ans[i+1]) ;
    }
    return 0 ;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:23:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   23 |     scanf("%d",&n) ;
      |     ~~~~~^~~~~~~~~
net.cpp:28:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   28 |         scanf("%d%d",&u,&v) ;
      |         ~~~~~^~~~~~~~~~~~~~

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