Submission #137107

#	Time	Username	Problem	Language	Result	Execution time	Memory
137107		silxikys	Network (BOI15_net)	C++14	63 / 100	2068 ms	57680 KiB

net

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
 
const int maxn = 5e5+5;
int n;
vector<int> adj[maxn];
int deg[maxn];
int tin[maxn];
int pt = 0;
 
void dfs(int i, int p) {
    tin[i] = pt++;
    for (int j: adj[i]) {
        if (j == p) continue;
        dfs(j,i);
    }
}
 
int main()
{
    scanf("%d",&n);
    for (int i = 0; i < n - 1; i++) {
        int a, b; scanf("%d %d",&a,&b);
        ++deg[a];
        ++deg[b];
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    vector<int> leafs;
    leafs.reserve(n);
    int start = 1;
    for (int i = 1; i <= n; i++) {
        if (deg[i] == 1) leafs.push_back(i);
        if (deg[i] > 1) {
            start = i;
        }
    }
    for (int j: adj[start]) {
        dfs(j,j);
    }
    sort(leafs.begin(),leafs.end(),[&](auto a, auto b) {
            return tin[a] < tin[b];
            });
    int k = leafs.size();
    int m = k/2;
    printf("%d\n",(k+1)/2);
    for (int i = 0; i < (k+1)/2; i++) {
        printf("%d %d\n",leafs[i],leafs[(i+m)%k]);
    }
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:22:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
net.cpp:24:24: 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: 0 / 37