Codeforces Round #635 (Div. 2) C.Linova and Kingdom

代码内容讲得比较清晰，慢慢细品吧··

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>
#include<queue>
#include<cstdlib>
using namespace std;
#define rep(i,l,r) for(i=l;i<=r;i++)
#define ll long long
const int INF = 0x7fffffff;
const int N = 1e6 + 7;
const int mod = 1e9 + 7;
struct node {
    ll b;
    ll id;
}h[N];
ll c[N];
vector<ll>G[N];
bool cmp(const node& a, const node& b)
{
    if (a.b == b.b)
        return G[a.id].size() < G[b.id].size();
    else
        return a.b > b.b;
}
ll n, m, t, x;
ll vis[N];
ll cnt[N];
ll dis[N];
int main()
{
    ll i, j, k;
    ll u, v;
    cin >> n >> k;
    rep(i, 1, n - 1)
    {
        cin >> u >> v;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    memset(vis, 0, sizeof(vis));
    x = 0;
    h[1].b = 0;
    rep(i, 1, n)
    {
        h[i].id = i;
        cnt[i] = 1;
    }
    vis[1] = 1;
    queue<ll>q;
    q.push(1);
    while (!q.empty())
    {
        ll start = q.front();
        q.pop();
        for (i = 0; i < G[start].size(); i++)
        {
            if (!vis[G[start][i]])
            {
                vis[G[start][i]] = 1;
                h[G[start][i]].b = h[start].b + 1;//计算深度

                q.push(G[start][i]);
            }
        }
    }
    rep(i, 1, n)
    {
        dis[i] = h[i].b;
    }
    sort(h + 1, h + n + 1, cmp);
    for (i = 1; i <= n; i++)
    {
        int now = h[i].id;
        for (j = 0; j < G[now].size(); j++)
        {
            if (dis[G[now][j]] > dis[now])
                cnt[now] += cnt[G[now][j]];
            //计算该节点的儿子们所做的贡献，即当该节点被标记时，统计该点后面儿子们所失去的总贡献
           // cout << cnt[now] << " " << cnt[G[now][j]]<<" ";
           
        }
       /* cout << endl;*/
        h[i].b -= (cnt[now] - 1);//若该点被标记，减去儿子后面的所做的贡献，记得-1减去本身
    }
    sort(h + 1, h + n + 1, cmp);

    ll ans = 0;
    rep(i, 1, k)
    {
        ans += h[i].b;
    }
    cout << ans << endl;

}
/*
20 7
9 7
3 7
15 9
1 3
11 9
18 7
17 18
20 1
4 11
2 11
12 18
8 18
13 2
19 2
10 9
6 13
5 8
14 1
16 13
*/