제출 #91871

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
91871		karma	Network (BOI15_net)	C++11	100 / 100	540 ms	59592 KiB

net

#include<bits/stdc++.h>
#define For(i, a, b)  for(int i = a, _b = b; i <= _b; ++i)
#define Ford(i, a, b) for(int i = a, _b = b; i >= _b; --i)
#define FileName      "test"
#define ll            long long
#define ld            long double
#define ull           unsigned long
#define Print(x)      cerr << #x << "is " << x << '\n';
#define pb            push_back
#define X             first
#define Y             second
//#define Karma

using namespace std;

template<typename T> inline void Cin(T &x)
{
    char c;
    T sign = 1;
    x = 0;
    for (c = getchar(); c < '0' || c > '9'; c = getchar())
        if (c == '-') sign = -1;
    for (; c >= '0' && c <= '9'; c = getchar())
        x = x * 10 + c - '0';
    x *= sign;
}
template <typename T> inline void Out(T x) {if(x > 9) Out(x / 10); putchar(x % 10 + '0');}
template <typename T> inline void Cout(T x, char c) {if(x < 0) putchar('-'); x = abs(x); Out(x); putchar(c);}
template <typename T, typename... Args> inline void Cin(T& a, Args&... args) {Cin(a);Cin(args...);}
template <typename T, typename... Args> inline void Cout(T a, char c, Args... args) {Cout(a, c);Cout(args...);}

typedef pair<int, int> pii;
typedef pair<ll, int> plli;
const int N = 1e6 + 7;

int n, u, v;
vector<int> res, a[N];

void Enter()
{
     Cin(n);
     For(i, 2, n)
     {
         Cin(u, v);
         a[u].pb(v), a[v].pb(u);
     }
}

void DFS(int u, int par)
{
    for(int v: a[u])
        if(v != par)
            DFS(v, u);
    if(a[u].size() == 1) res.pb(u);
}

void Solve()
{
     For(i, 1, n) if(a[i].size() > 1) {DFS(i, i); break;}
     int sz = res.size();
     cout << (sz + 1) / 2 << '\n';
     for(int i = 0; i * 2 + 1 < sz; ++i) cout << res[i] << ' ' << res[i + (sz + 1) / 2] << '\n';
     if(sz & 1) cout << res[sz / 2] << ' ' << res[0] << '\n';
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
#ifdef Karma
    freopen(FileName".inp", "r", stdin);
    freopen(FileName".out", "w", stdout);
#endif // Karma

    Enter();
    Solve();

    return 0;
}

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